as Cape Turakirae and Kaikoura, although of intermediate size, are 93% and 100% branched respectively.

A similar trend in diminishing size, but not branching since the genus is stolonal in habit and each erect stem bears a single hydranth, was determined from collections of Silicularia. It was noticed that on the short erect stems of colonies from north of about 41° S. there were only short hydrothecae; and the hydrothecae were much larger on the tall erect stems of colonies from sub-Antarctic islands. Material from the intermediate region, that is the South Island and up to 41° S., consisted of colonies of tall erect stems and long hydrothecae, colonies of short erect stems and short hydrothecae, and also colonies of short and tall erect stems with short or long hydrothecae corresponding to the length of the stem. Colonies with only short stems were found in the warmer harbour waters.

Colonies of Silicularia with short erect stems, small hydranths and short hydrothecae are not growth stages of colonies with tall erect stems, large hydranths and long hydrothecae, as the former have reached full functional differentiation Berrill (1950) in studies on Clytia johnstoni (another species with stolonal growth) has shown that when the terminal hydranth on an erect stem has become functional, the stem has reached its full height, also that when a hydranth becomes functional growth ceases so that small functional hydranths are not an early stage in the growth of large ones. These facts fit well to the data recorded here for Silicularia since it can be accepted that the low erect stems from northern waters which have only functional hydranths have reached their full height. Likewise, that small fully functional hydranths do not grow further.

The length of hydrotheca in Silicularia has been utilised extensively in the determination of the species of the genus. Two species, S. bilabiata (Coughtrey, 1875) and S. campanularia (von Lendenfeld, 1883) have been previously recognised from New Zealand by Bale (1924). These each correspond to material from the southern and northern regions of New Zealand. S. bilabiata as understood by Bale was a species having long, narrow hydrothecae up to 1.0 mm in length, and S. campanularia having short hydrothecae not more than 0.67 mm in length. Material from Sumner, Christchurch and Island Bay, Wellington shows hydrothecae of both these sizes on the erect stems of the one colony. Accordingly it is clear that his two species are forms of the one species, which is here recognised as S. bilabiata. Reference to the other seven species in the genus shows that formerly six of these were in the main distinguished by the size of the hydrothecae and the number of species in the genus can now be reduced to three.

The geographic latitudinal distribution of tall, intermediate and short hydrocauli of both O. geniculata and Silicularia in New Zealand is in agreement with the sub-Antarctic, intermediate and subtropical sea-surface temperature zones recognised by Fleming (1944). It can then be concluded that height and branching in O. geniculata and height in Silicularia is related to geographic latitude and temperature, and probably other factors as indicated by the differences in harbour and offshore colonies from the intermediate zone.

The variations in height and form, however, do not show a complete cline because of abrupt water climate changes in the New Zealand region. New Zealand is unique in its relation to the water masses of the southern hemisphere (Figs. 1 and 2). The Antarctic and Subtropical Convergences extend further northward and southward respectively in the New Zealand region than in any other, and themselves “converge” at the Chatham Islands. Cold sub-Antarctic water lies below the South Island, mixed cold and warm waters are found intermediate between the two Convergences around the South Island and southern North Island, and subtropical water from approximately 41° S. northward in the North Island.

As New Zealand material of O. geniculata and S. bilabiata can be readily recognised from sub-Antarctic, intermediate and subtropical zones, colonies from these

culata from below latitude 48° S. are approximately 8 times the size of those from the far north above latitude 38° S., and also the former show 100% branched colonies as against the latter, which show 100% simple, unbranched colonies. The internode length also, as might be expected, follows the same trend as the overall size, so that colonies from the south show internodes about 2 to 3 times (0.68 mm to 0.93 mm) the length shown by those in the far north (about 0.38 mm). Gonotheca on colonies from latitude 48° S. to 41° S. vary in size within fairly narrow limits, being 0.75 mm to 0.90 mm in length and 0.25 to 0.31 mm in breadth, while colonies from approximately 37° S. latitude to 34° S. possess gonotheca smaller in size, 0.62 to 0.75 mm in length and about 0.25 mm in breadth, thus showing the trend to smaller size in the more northern waters. It is relevant to note that Fell (1953, pp. 106–7) records that the echinoid Pseudechinus novae-zelandiae (Mrtsn.) increases in size from north to south in New Zealand, the smallest forms being found in Cook Strait, intermediate off Otago, and largest from sub-Antarctic islands.

The above evidence demonstrates that in the southern hemisphere O. geniculata attains maximum growth in high latitude, and that in its northward distribution towards warmer waters there is a marked decrease in overall size, and loss of a branched habit. In fact, colonies from the subtropical waters of northern New Zealand are to be called “diminutive” compared with those of the far south. However, samples from intermediate points between the two extremes also suggest that the difference in form throughout the region may not be solely due to their latitudinal position. If latitude is the only factor influencing the nature of the branching and the size in O. geniculata, it seems that in relation to decreasing latitude samples would show a complete cline from south to north.

Such is not the case, and the intermediate zone, with its mixed cold sub-Antarctic and subtropical water (Fleming, 1944) shows most clearly the break in cline due to different water temperatures. It is recognised that harbour waters show a wider temperature range and are rather warmer than are open ocean waters, and this is reflected in the lower percentage of branched hydrocauli found in Dunedin Harbour and Wellington Harbour than in colonies from off Cape Turakirae, Kaikoura and the Chatham Islands. Material outside Christchurch Harbour from Menzies Bay (Fig. 1a) is not fully grown, and it is anticipated that a higher percentage of branched hydrocauli, in line with the percentages known from Kaikoura and the Chatham Islands, will be shown when the hydrocauli attain full height.

Also, samples from Cape Turakirae, the Chatham Islands, and Christchurch give evidence that the hydrocaulus reaches a certain minimum height before branching commences, and so demonstrates that branching is secondary to height. Hydrocauli below 10.0 mm are rarely branched, those between 10.0 mm and 15.0 mm are usually slightly branched, and those above 15.0 mm show one or more branches. Branching is just commencing in the Christchurch material, and one or two secondary hydranths or a branch with two or three hydranths can be seen growing from the axils of the primary hydranths.

Berrill (1948, p. 94), working with O. geniculata, O. articulata and O. longissima found that temperature was a controlling factor in the seasonal appearance of these species, that they disappeared and reappeared respectively as the temperature rose and fell markedly above and below 20° C., and that hydranths do not start to form in O. commissularis unless the temperature is below 20° C. (Berrill, 1949, p. 254). O. geniculata is not seasonal in Wellington Harbour, but such a condition does not altogether conflict with Berrill's findings when it is known that the maximum temperature recorded for Wellington Harbour is about 19° C. and the mean for the year about 14° C. Temperature, then, would not be a prohibitive factor in Wellington, and probably O. geniculata occurs all the year round in latitudes south of Wellington, but is seasonal in occurrence in the Auckland area and latitudes further north where the maximum sea surface temperature is about 21° C. There

is no doubt, also, a minimum temperature giving seasonal occurrence in very cold waters. The fact that most of the present material was collected in summer during the upper temperature range, and that the majority of the hydrocauli in some samples, notably Christchurch, and the Chatham Islands, were not fully grown, may mean that the sizes given in this paper are not the maximum attainable by the species in New Zealand and adjacent waters. There are a few hydrocauli of O. geniculata that support this view in a collection of hydroids from the Auckland area and kindly placed at my disposal by Mr. Kulka and Mr. Trevarthen. The specimens were taken in June, and are fully grown with a maximum height of 10.0 mm. This, however, is of relative importance only, and would not affect the observed trend from large to small colonies with a change of latitude from south to north.

O. geniculata from subtropical water in S. America is very similar in size range and habit to the New Zealand material from latitude 34° S. Mendes (1946, p. 591) says that his material of O. geniculata from Santos, Brazil, just north of the Subtropical Convergence on approximately latitude 23° S., “is peculiar on account of the small size” (rarely above 10.0 mm) “of the colonies, their lack of ramification, and the small size of the gonangia” (0.58 to 0.75 mm in length and 0.25 to 0.28 mm in breadth).

The Subtropical Convergence lies below Tasmania in Australian waters, so that the influence of warm subtropical water will be seen in higher latitudes than in New Zealand. This assumption is strengthened by records of O. geniculata from Tasmania and the East Australian coast. Hodgson (1950) describes simple, unbranched hydrocauli of intermediate size (up to 20.0 mm) from Tasmania, and Bale (1894, p. 99) small unbranched colonies about 4.0 mm from Port Phillip Bay, Melbourne. Port Phillip Bay is on a similar latitude to Wellington but colonies in the latter harbour show by their height (15.0 mm) the influence of the cold sub-Antarctic element of the intermediate mixed water zone. O. geniculata is not known from the Brisbane, Great Barrier Reef region (Blackburn, 1942) which suggests that the minimum water temperature in this region is too high for settling and growth.

Descriptions of O. geniculata from localities other than the Antipodes Is. in the sub-Antarctic zone gives further evidence that temperature and latitude affects form and height. Tall colonies with branched and unbranched stems are recorded by Hickson and Gravely (1907, p. 30) from Auckland Islands (Fig. 1a) and Allman (1888, p. 23) from Kerguelen Island (Fig. 2, locality 5). The percentage of branched to unbranched hydrocauli is not given, but there seems little doubt that the percentage of branching was high, as Hickson and Gravely select out this character as one worthy of note, as it is in contrast to northern hemisphere material, which is usually unbranched. Other Kerguelen material (Australian Nat. Ant. Exped.) strengthens this conclusion, as from 100 hydrocauli 80% are extensively branched. Also the stems were still growing, so that the percentage of branched stems in the colony will probably exceed 80% when maximum height is attained.

The change in colony form discussed above is not of importance for specific determination in Obelia geniculata as it is at present defined, because the variation of diagnostic characters is not affected and the characters are as easily distinguished in specimens 5.0 mm in height as in those 8 times the height and freely branched. O. geniculata has not yet been described as attaining such a large size or showing such a range of branching in northern hemisphere waters (Hickson & Gravely, 1907, p. 30; Fraser, 1946, p. 224, and Berrill, 1948, p. 94). Although not of immediate use for specific determination, the study gives a widened concept of the species and three new forms can be recognised.

Consequent from the above, Obelia geniculata must now be defined as follows:–

Hydrocaulus, monosiphonic, simple, or irregularly branched, and branches half or more of the length of the main stem, which is up to 40.0 mm in length; flexuous,

but bilaterally symmetrical with narrow and broad sides, variable in outline, the two broad sides usually forming erect convex lobes, the narrow sides lower, forming two “lips”, one lower than the other, when viewed from the broad side, and lips may appear slightly everted; the interior of the hydrotheca nearly fully occupied by perisarc but pierced by the “hydropore” which is enlarged proximally just above the spherical annulus and widens out above into a shallow cavity; colonies dioecious, hydrothecae of male and female colonies tend to differ in size, in the length to breadth ratio, and in the angle of slope of the margin; short hydrothecae of female colonies usually have a length to breadth ratio averaging 1:1, while in the longer hydrothecae the average is in the order of 1.30:1, the angle of slope of the oblique margin is between 20° and 30°; range of hydrothecal length in the female colony is 0.40 to 1.43 mm; in male colonies the hydrothecae are usually broader than long, the length to breadth average is approximately 1:1.6, and this is reflected in the smaller angle of slope of the margin which ranges from 8° to 20°; range of hydrothecal length in the male is 0.30 to 0.90 mm; hydranths occupy the shallow concavity of the hydrotheca and possess a flattened base with a protrusion fitting into a notch or sinuation halfway down the inside of the hydrotheca on the higher side; and possess a large rounded retractible body “caecum”; tentacles from about 20 to 40 in number, small hydranths have smaller tentacles and fewer tentacles than large hydranths; nematocysts on the tentacles in rings; gonothecae—male and female arise from the stolon, frequently 5 to 7 in a row about 0.30 mm apart, or scattered irregularly on the stolon; male gonothecae taller, narrower, and with a longer pedicel than the female; gonothecae of both sexes change shape from young to the old condition, but the change of shape is more conspicuous in female colonies; in young gonothecae the distal end is more truncate, and in the female this end is also the region of maximum width, and is slightly convex; as the gonothecae grow the distal end becomes more tapered; walls of gonothecae of both sexes are thickened, but not in the immediate vicinity of the aperture; perisarc 0.062 to 0.18 mm in thickness and thrown into shallow waves, but internal and external waves do not always correspond in position; male gonothecae rather tubular, 2.5 mm to 4.0 mm in length, 0.31 to 0.43 mm in width, with a pedicel 0.65 to 0.88 mm in length and 0.125 to 0.19 mm in width; female gonothecae compressed, with broad and narrow sides, 2.0 to 3.0 mm in length, 0.70 to 1.25 mm in width in broad view and pedicel 0.37 to 0.75 mm in length and 0.125 to 0.31 mm in width; female reproductive zooid produces a large and small eumedusoid without mouth and digestive cavity; the ova develop in regular rows along almost the whole length of the branched radial canals; the canals are dark-brown in colour with brown pigment granules; male reproductive zooid produces a single more elongate eumedusoid; eggs, planulae, and the method of liberation of the sexual products inadequately known but short gonothecae up to 2.0 mm in length have eggs approximately 0.20 mm in diameter, and planulae about 0.37 × 0.20 mm when liberated. Type locality: “Fuci, 1 to 3 fathoms, Timaru (N.Z.); delicate seaweeds; growing from the roots of Laminarians.”

The following new forms can now be recognised:

forma subtropica (= S. campanularia (von Lendenfeld, 1883)).

Range, northward of the Subtropical Convergence and in the milder harbour waters of the intermediate zone; stem smooth, or very slightly undulated, hydrothecae short, 0.30 to 0.67 mm in length: gonotheca—female, about 2.0 mm in length and about 0.70 mm in width, pedicel up to 0.37 mm in length; male, up to 2.5 mm in length and 0.43 mm in width, pedicel about 0.65 mm in length.

forma intermedia.

Range, between the Subtropical Convergence and Antarctic Convergence and usually in offshore waters; long hydrothecae (female 0.67 to 1.43 mm; male, 0.67 to 0.90 mm in length) and short (0.30 to 0.67 mm in length) on the same stolon: gonothecae, same size range as in forma subtropica.

forma subantarctica.

Range, offshore waters of the intermediate zone, and southward of the Antarctic Convergence; hydrothecae long (female 0.67 to 1.43 mm; male 0.67 to 0.90 mm in length): gonothecae—female, about 3.0 mm in length, 1.25 mm in greatest width and pedicel 0.75 mm in length; male, about 4.0 mm in length, 0.31 mm in width and pedicel about 0.88 mm in length.

No holotype of S. bilabiata was designated by Coughtrey. The writer suspects that a slide labelled Campanularia bilabiata Coughtrey, Timaru, from the Hutton “Type” collection, is either the type or syntype of Silicularia bilabiata since Coughtrey (1875, p. 281) acknowledges the assistance of Hutton's type collection, which was placed at his disposal, and the “loan of some specimens which he (Hutton) had recently collected”. Coughtrey unfortunately does not give the source or name of collector of his material of S. bilabiata. The writer nominates the slide Campanularia bilabiata Coughtrey, locality Timaru, Hutton “Type” Collection, as the lectotype. (Canterbury Museum, Christchurch, Hydroid collection Slide No. 1.) Material compared with the designated type and regarded as identical is lodged in the Zoology Department, Victoria University College, Wellington.

In geographical position New Zealand lies across the line that is known to limit the spread of several southern circumpolar species, and as Moore (1953, p. 5) says, “if the limits can be fixed for a single species, or phases in any one life history here (N.Z) and on the Tasmanian or Southern Australian coasts it may be possible to decide to what extent sea-surface temperature as given in tables are correlated with distribution”. The distribution of the forms of S. bilabiata appears to provide an example of a species which is an indicator of the major water masses since the Subtropical Convergence marks, so far as is known, the northern limit of colonies with only long hydrothecae, while colonies with only short hydrothecae are found in subtropical waters excepting only their restricted occurrence in semi-enclosed harbour waters S. bilabiata forma subtropica (= S. campanularia) and S. undulata are known from Australian waters. S. undulata is distinguished from S. bilabiata by its distinctly undulated pedicel. S. bilabiata occurs in Australia up to Sydney, N.S.W. and Lord Howe Island, and conforms to the findings for New Zealand. The Subtropical Convergence lies below Tasmania (Fig. 2). Therefore, although within similar latitudes to those of New Zealand, colonies of S. bilabiata from Australian coastal waters are of small size with short hydrothecae. This can be taken as demonstrating that temperature and not latitude is the significant factor. In contrast, tall colonies with only long hydrothecae seem to flourish in waters where the mean annual sea-surface temperature is not higher than about 14° C. Such conditions are found southward of the Subtropical Convergence.

The study of S. bilabiata (Coughtrey, 1875) in New Zealand and Australia gives evidence of the greatest value in the determination of the status of the southern hemisphere species of Silicularia which are not well distinguished from one another or from S. bilabiata. It will be demonstrated below that these “species” appear to have been separated out on a size difference which was not recognised as related to the temperature effect of the major water masses and to differences in latitude. Also, much of the confusion has been caused by the inadequate descriptions of S. bilabiata.

S. repens (Allman, 1876) recorded by Allman from Swain's Bay, Kerguelen (Fig. 2, locality 5) and by Marktanner-Turneretscher (1890) from South American off-shore waters (48° S. lat. 64° W. longit., locality 13) is regarded by these authors as having the following characters: stolons more or less parallel with some reticulation between; hydrothecal pedicel tall, up to 8.0 mm, smooth, with a single globular structure between the pedicel and the base of the hydrotheca; hydrotheca bilaterally symmetrical with oblique margin, long, about 1.0 mm or over in length: gonothecae—scattered, not closely aggregated, male and female on the one stolon; male tall, tubular, about 4.0 mm in length and 0.31 mm in width, with small distal circular aperture; female shorter, somewhat compressed, about 3.0 mm in length, broad,

about 1.2 mm in width, distal end more truncate than male and with wide aperture. The above characters are those of S. bilabiata forma subantarctica except that S. bilabiata is dioecious. Kerguelen is located in sub-Antarctic water. Marktanner-Turneretscher's material came from the zone of intermediate waters and presumably from either a shallow bank or from some floating object, since the plotted location is off-shore, and in this sense the material is like the forma subantarctica recorded from the open coast at Timaru, N.Z. Allman (1888, p. 26) says that S. repens “may” be monoecious as male and female gonothecae are on the same stolon. To the naked eye the male and female gonothecae of S. bilabiata forma subantarctica from Macquarie Island (sub-Antarctic zone, locality 4) appear to arise from the same stolon, but dissection under the low power microscope shows that although the stolons of one sex may cross and recross that of the other with some adherence of their perisarc, the coenosarc of the one sex is not continuous with that of the other. In specimens of S. bilabiata forma intermedia from Wellington, the stolon of one sex terminates in a cross-shaped process (Fig. 2f) where it meets that of the other sex. Allman possibly looked at the stolons of his specimens with the naked eye or a hand-lens, and obtained the impression that the species was monoecious. Hartlaub (1905, p. 572), speaking of the “pretended” monoecious behaviour of S. repens and S. atlantica (Marktanner-Turneretscher, 1890, Pl. 3, Fig. 14), says that mistakes are easily possible as the stolons of the rhizome stretch sometimes close to or over each other (Transl.). Hartlaub concludes from his study of Silicularian material at Hamburg that the genus Silicularia is dioecious. The evidence of material from New Zealand and Macquarie Island strengthens this opinion. In all other aspects—namely, of size, shape of gonothecae, etc., and in its known range in relation to the major water masses, S. repens is similar to S. bilabiata forma subantarctica and is here considered a synonym of that species.

S. aggregata (Allman, 1888) recorded from Kerguelen Island by Allman (1888) (Fig. 2, locality 5) is described by him as having the following characters: Stolons reticulate; hydrothecal pedicel tall, up to 8.0 mm, smooth with single globular structure between the pedicel and the base of the hydrotheca; hydrotheca bilaterally symmetrical with oblique margin long, 1.4 mm in length: gonothecae—densely crowded, only female gonothecae known and these about 3.5 mm in total length, and of similar shape to those of S. repens. S. repens (= S. bilabiata forma subantarctica) and S. aggregata were separated out by Allman because S. repens has parallel stolons, is monoecious and with scattered gonothecae, while S. aggregata has reticulate stolons, is dioecious and with densely crowded gonothecae. Both species are from the same locality. The character of the stolons and the density of the gonothecae are variable features in all forms of S. bilabiata and are unrelated to latitudinal location or water temperature. The pattern made by the stolons, however, is related to the texture of the substratum on which the hydroid grows. This is clearly shown by S. bilabiata forma intermedia from Island Bay, Wellington. Colonies growing on Macrocystis pyrifera, a species in which the lamina has distinct and deep corrugations, shows parallel stolons which follow closely the valleys of the seaweed lamina (Fig. 2, e). The shape and the extent of the valley determines the spacing of the stolons and hence in large measure the density of the erect stems and gonothecae. For example, if the valley sides slope inwards the stolons may overlap and at maturity rows of closely packed gonothecae can be seen. The stolon pattern of S. bilabiata on Marginariella boryana is in sharp contrast. The lamina is smooth, and the stolon pattern forms an open network (Fig. 2, c). These two patterns appear to be the extremes. Stolon reticulations of S. bilabiata are much closer together on the inner margin than on the flat surface of the lamina of M. boryana, and they twine and loop the sticklike reproductive branchlets. Material of S. bilabiata forma subantarctica from Kerguelen, growing on Macrocystis pyrifera, shows parallel stolons in the valleys, while that from Macquarie Is., on a smooth

surfaced brown alga has reticulated stolons. Hartlaub (1905) considered that the pattern of the stolons in species of Silicularia was an unreliable character for use at the specific level. It is clear, then, from the above, that the characters of S. aggregata, and its known range in relation to the major water masses, reduce it to a synonym of S. bilabiata where it agrees with the forma subantarctica.

S. hemispherica (Allman, 1888), recorded by Allman from Port William, Falkland Islands (Fig. 2, locality 11); by Hartlaub (1905) from Port Toro, Navarin Island, Tierra del Fuego Archipelago (locality 14) and Ritchie (1907) from Gough Island (locality 7) is accepted by these authors as having the following characters: stolons more or less parallel with a few reticulations between; hydrothecal pedicels both tall and short, smooth, with a single globular structure between pedicel and the base of the hydrotheca; hydrotheca bilaterally symmetrical with oblique margin; hydrothecae of colony may be all short, not more than 0.67 mm in length (Allman), or some long (about 1.0 mm) and some short (Hartlaub): dioecious; male and female gonothecae of same shape as those of S. repens and S. aggregata (Hartlaub, 1905, Figs. A² and Z¹) but half the size, the male being about 2.5 mm and the female about 2.0 mm in length. Young female gonothecae differ from the fully grown gonotheca in having a wide distinctly truncated distal end. The above characters are those of S. bilabiata forma subtropica (colonies with only short hydrothecae) and S. bilabiata forma intermedia (colonies with both long and short hydrothecae). S. hemispherica occurs in harbour waters and open ocean water in the intermediate zone, as do forma subtropica and forma intermedia of S. bilabiata.

S. georgiana (Pfeffer, 1889) recorded by Pfeffer from S. Georgia (Fig. 2, locality 10) and by Broch (1929) from Crozet Island (locality 6) is distinguished on the following characters: hydrothecal pedicels tall, up to 8.0 mm, smooth, with single globular structure between pedicel and base of hydrotheca; hydrotheca bilaterally symmetrical with oblique margin, long, 1.0 mm or over: dioecious; gonothecac—male and female the same size range and shape as S. repens and S. aggregata; male and female reproductive zooids produce eumedusoids. Young female gonothecae differ from fully grown in having a wide distinctly truncated distal end. These are characters of S. bilabiata forma subantarctica and the known range of S. georgiana in relation to the major water masses is similar to forma subantarctica.

S. atlantica (Marktanner-Turneretscher, 1890) recorded from off Cape San Roque (Fig. 2, locality 9) was described as a small species with the following characters: stolons more or less parallel with a few reticulations between; hydrothecal pedicels short, not more than 6.0 mm and usually less, smooth, with a single globular structure between pedicel and hydrotheca; hydrotheca bilaterally symmetrical with oblique margin, short, 0.35 to 0.60 mm in length; monoecious; gonothecae short; male, 1.7 mm in length and 0.25 mm in width in expanded region, pedicel 0.38 mm in length; female up to 2.7 mm in total length, 0.67 mm in breadth; shape of both male and female gonothecae as for S. repens and S. aggregata. The characters of the hydrotheca and female gonotheca are those of a fully grown female colony of S. bilabiata forma subtropica. The length and shape of the male gonothecae show them as juvenile, which accounts for their being slightly shorter than the female gonothecae instead of longer as is usual. The supposed monoecious character of the colonies of S. atlantica are discussed above under S. repens. S. atlantica inhabits the same major water mass as S. bilabiata forma subtropica.

S. pedunculata (Jäderholm, 1904) recorded from the S. Shetland Is. by Jäderholm (Fig. 2, locality 12), by Hartlaub (1905) (= S. divergens) from S. Georgia (Fig. 2, locality 10) and Fraser (1938) off Secas Islands, Panama (Fig. 2, locality 15) is regarded by these authors as having the following characters: stolon reticulate, hydrothecal pedicel slender 1.5 mm to 8.0 mm in length, smooth, slightly undulated or entirely undulated, with single globular structure between pedicel and base of

hydrotheca; hydrotheca radially symmetrical, walls distally thickened in the proximal region (as in Orthopyxis caliculata) thinning towards the margin; margin entire, smooth not oblique: dioecious, female gonotheca elongate, fusiform, tapered proximally and distally, with a distinct long pedicel irregularly undulated or undulated throughout; young gonothecae with distal end truncated.

S. pedunculata is not a synonym of S. bilabiata. The radially symmetrical hydrotheca, the shape of the female gonotheca and the distinct pedicel of the gonotheca have long been recognised as unique within the genus. Nutting (1915, p. 91) says of S. pedunculata, “the character of the gonosome indicates that this is a Silicularia. In other respects it is a Eucopella” (= g. Orthopyxis). Fraser (1946, p. 206–7), when discussing the status of Silicularia and Eucopella, regards the genus Silicularia as one in which the “gonophores produce fixed sporosacs similar to those in Campanularia” in contrast to Eucopella in which the reproductive zooids produce “large medusoid structures devoid of mouth and digestive cavity”. It will be shown below that separation of the genera Silicularia and Orthopyxis (= g. Eucopella) depends not on the structures produced by the reproductive zooid as these are similar, but on the characters of the hydranth and hydrotheca which are quite distinct.

The reproductive zooid gives rise to unmistakable male and female eumedusoids in S. bilabiata (Fig. 3, a, b and c) and S. georgiana (Broch, 1929, Figs. 11 and 12) Figures of the reproductive structures of S. reticulata (Hartlaub, 1905, p. 569, Fig. R¹, C) and S. undulata (Mulder & Trebilcock, 1914, Pl. 2, Fig. 7), although lacking in detail leave little doubt that eumedusoids are also produced in these two species. Illustrations of other species of Silicularia, however—namely, S. atlantica (Marktanner-Turneretscher, 1890, Pl. 3, Fig. 14) and S. hemispherica (Hartlaub, 1905, p. 578, Fig. 2) show only planulae and/or large eggs within the gonotheca, thus giving the impression that the reproductive zooid gives rise to a sporosac as in Campanularia. Some female colonies of S. bilabiata forma subtropica from Dunedin (Fig. 3, j) show ova and planulae similar to S. atlantica and S. hemispherica, but other material from Dunedin (Fig 3, i) and also that of forma subtropica from New Plymouth, shows that eggs and planulae within the gonotheca is only a more advanced stage of maturity of the gonophore. This suggests that in S. bilabiata and most probably other species of Silicularia, the maturation of the gonophore is similar to that known for Campanularia integra where at one season it is eumedusoid and sessile and at others breaks loose as a “defective medusa” (Broch, 1918, p. 160).

From all these observations it seems reasonable to conclude that the structure produced by the reproductive zooid in Silicularia is a eumedusoid, not a sporosac, the character retained by Fraser (1946) to distinguish Silicularia from Orthopyxis. Therefore Silicularia and Orthopyxis can no longer be separated out on the character of the reproductive structures and S. pedunculata with its radially symmetrical hydrotheca with a cavity deep enough for the complete retraction of the hydranth, and a hydranth without a caecum, possesses the characters of Orthopyxis not Silicularia in which the hydrotheca is bilaterally symmetrical with a cavity not deep enough to allow the complete retraction of the hydranth and a hydranth with a distinct caecum. Further, the reproductive structures, although inadequately described and figured for S. pedunculata, are recognisable as eumedusoid in character (Nutting, 1915, Pl. 24, Fig. 8). S. pedunculata (Jäderholm) is here recognised as O. pedunculata (Jäderholm).

The genus Orthopyxis needs revision but O. pedunculata seems a good species as the nature of the female gonothecae is narrow and elongate, not truncate as in most other species of the genus, and its pedicel is longer and undulated. It is most closely allied to Campanularia (Orthopyxis) norvegiae Broch 1948, a species also known from S. Georgia, but the marginal thickening “so characteristic of O. norvegiae” is absent in O. pedunculata and the pedicel of the gonotheca is longer. It should be noted that Fraser's (1938) material from off Panama was infertile, so

that it cannot with certainty be assigned to O. pedunculata, as the erect stems and hydrothecae of O. pedunculata resemble closely those of the variable and ubiquitous O. caliculata.

S. reticulata (Hartlaub, 1905) recorded from Port William, Falkland Island (Fig. 2, locality 11) has the following characters: stolon reticulate, hydrothecal pedicel short, not greater and usually less than 6.0 mm, smooth, with single globular structure between pedicel and base of hydrotheca; hydrotheca bilaterally symmetrical with oblique margin, short, not more than 0.67 mm in length; dioecious; female gonotheca about 2.0 mm in length and with single “gonophore”, male unknown. The above characters are those of S. bilabiata forma subtropica, and S. reticulata inhabits harbour water in the intermediate zone as does forma subtropica.

S. undulata (Mulder & Trebilcock, 1914) recorded from South Australia, Victoria and N.S.W., Australia (Fig. 2, locality 2) has the following characters: stolon reticulate; hydrothecal pedicels of variable length, undulating, stout generally thickened at the base, a single globular structure between pedicel and base of hydrotheca; hydrotheca bilaterally symmetrical with oblique margin, short, not more than 0.67 mm in length; gonothecae about 1.0 mm in length, decumbent, about as long as broad, flat underneath, convex and transversely rugose above, aperture terminal; pedicel very short. The gonothecae of S. undulata closely resemble those of S. bilabiata forma subtropica from Bethells, Auckland, but the undulations of the hydrothecal pedicels of the former species are far more prominent than that shown by the New Zealand material from Bethells (Fig. 2, d) or indeed of any other New Zealand form of S. bilabiata, and determine S. undulata as a distinct species.

Briefly, S. repens, S. aggregata and S. georgiana with long hydrothecae and tall gonothecae are synonyms of S. bilabiata and can be recognised as the forma sub-antarctica; S. hemispherica (Allman's material), S. atlantica and S. reticulata with short hydrothecae and short gonothecae are synonyms of S. bilabiata and are the forma subtropica; while S. hemispherica (Hartlaub's material), with long and short hydrothecae on the one colony and short gonothecae, is a synonym of S. bilabiata and is the forma intermedia. S. undulata is a distinct species and S. pedunculata is Orthopyxis pedunculata.

S. bilabiata is very closely related to S. rosea Meyen, 1834, the genotype recorded by Meyen from Staten Island, Tierra del Fuego (Fig. 2, locality 14) and S. Georgia (locality 10); by Jäderholm (1905) from Falkland Islands (locality 11) and by Vanhoffen (1910) from Tristan da Cunha (locality 8). Hartlaub (1905) after examination of the genotype in Berlin Museum, describes the species as follows: Parallel stolons that may aggregate and fuse together, hydrothecal pedicel smooth, with a conical rejuvenation at the base, a single sphere between the distal end of the stem and the base of the hydrotheca; hydrotheca bilaterally symmetrical, with oblique margin, sometimes elongated, sometimes short: dioecious; female gonothecae tubiform, relatively short, about 2.0 mm, pedicel indistinct with conical point at base, may be slightly undulated in side view.

The forma intermedia of S. bilibiata has the characters described for S. rosea if in S. rosea the long and short hydrothecae occur on the stems of the one colony, and if the conical regeneration at the base of the hydrothecal and gonothecal pedicel is a variable and not a constant character. Unfortunately Hartlaub's description is not clear on these points, and his Figs. T¹ and X¹ do not show the conical terminations. Regenerations giving the hydrothecal stem a jointed and hence “conical” appearance are well known for S. bilabiata, but they are of irregular occurrence. Other material collected by Zschau from S. Georgia (sub-Antarctic zone, locality 10) and recorded by Meyen as S. rosea (cf. Hartlaub, p. 575, Fig. X¹) suggests that some colonies of S. rosea have only long hydrothecae and tall gonothecae. If so, S. bilabiata forma subantarctica resembles S. rosea from South Georgia. It is significant that Hartlaub (1905) considered it likely that S. aggregata, S. georgiana and S. repens,