C. nilsoni has been known only from the holotype, a male 1,030 mm long, taken in deep water off Kaikoura, New Zealand, in 1928, and a second specimen recently recorded from south-eastern Australia by Cowper and Downie (1957, p. 9, and Appendix p. 7). C. foliaceus is known from at least four specimens, 325 mm to 407 mm long, from japan and the Philippines, in depths of 345 fathoms to 960 fathoms, while Richardson's (1956, p. 7) illustration of a specimen^* from Kaikoura extended its known range to New Zealand.

The present study of these two species is based on the holotype of C. nilsoni (preserved in the Canterbury Museum, but in a very desiccated condition); a second New Zealand specimen referable toC. nilsoni, a female 1,370 mm long from 500 fathoms off Kaikoura; and eight specimens seemingly C. foliaceus, 438 mm to 515 mm long, also taken off Kaikoura in 200 fathoms. The capture of all these specimens other than the holotype is due to Mr. Richard Baxter of Kaikoura, whose co-operation in carrying out experimental line-fishing in deep water during 1954 and 1955 is greatly appreciated.

Comparison of the second New Zealand specimen of C. nilsoni with the holotype shows no significant differences. Their proportional dimensions, expressed as percentages of total length, agree very closely, as shown in Table I, columns E and F. The extended posterior corner of the pectoral fin is longer in the second specimen, being 1/9th of the length of the fin compared with 1/12th in the holotype. The dorsal fin spines of both specimens are comparatively short, but close examination shows that they have a worn or eroded appearance. If this is the case, it may be the explanation for the fact that the 2nd spine is shorter than the 1st in the holotype, whilst the reverse holds true for the second specimen and is the usual condition for other species in the genus. Both the upper and the lower teeth of the holotype are slightly more erect than those of the second specimen; and while there is a symmetrical, median lower tooth in the holotype, its equivalent is oblique in the second specimen. Similar variation in this latter feature is recorded for C. squamosus and C. uyato (Bigelow and Schroeder, 1957, p. 72). The cusps of the lower teeth in both specimens have irregularly and finely serrate cutting edges (Text-fig. 2, H, as C. squamosus), which is also a feature of other species in the genus. But the same condition occurs in the cusps of the upper teeth (Text-fig. 2, G, as C. squamosus), some of which in both the functional and the reserve series of both specimens show traces of irregular serration of their cutting edges, particularly at the shoulders of the cusps. This feature is not as prominent, nor as general in the upper teeth as it is in the lower, and because of the smaller size of the upper teeth, is readily overlooked. It is not known for other species of the genus except for C. granulosus as figured in Bocage and Capello (1866, Pl. 1, Fig. 3, E), though Bigelow and Schroeder (1957, p. 67) report that the upper teeth in two specimens of C. granulosus that they have examined are smooth. The dermal denticles of both specimens are scale-like (Text-fig. 3, as C. squamosus), subovoid in shape, each with three longitudinal ridges, and terminating in a sharply pointed median tooth which is flanked on either side by one to several small, irregular lateral teeth; the number of these lateral teeth is greater in the second specimen than in the holotype, but in all other features the denticles are the same.

The New Zealand specimens referable to C. foliaceus agree closely with the description and illustrations of the holotype of this species. The range of proportional dimensions expressed as percentages of the total length of five of these specimens is shown in Table I, column C, for comparison with those of the holotype, column B, and a smaller specimen from Japan, column A. Furthermore, Mr. N. B. Marshall of the British Museum, who has compared one of the New

Zealand specimens, a female 462 mm long, with the holotype, and who has checked on the details of the teeth, denticles, fins, fin-spines and preoral clefts, reports that he can find no differences between them (personal communication). The condition of the posterior corner of the pectoral fin, which in the holotype is so little extended that it is best described as quadrate, is matched in some of the New Zealand specimens; but in others the extension is well marked so that its length approximates to 1/20th the length of the fin (Text-fig. 1, A). One feature of some of the New Zealand specimens, which does not occur in the 351 mm male from Japan described by Bigelow and Schroeder (1957, p. 78) and apparently not in the holotype either, is the presence of irregular and fine serrations on the cutting edges of the lower teeth (Text-fig. 4, J, as C. squamosus). The extent to which these are present, in both the functional and reserve rows, is about the same as in the specimens of C. nilsoni, but they are most prominent only in the teeth of the larger specimens of C. foliaceus. The upper teeth are generally smooth, but as they are so small, such irregularities as are present on their cutting edges could as equally be described as serrations as could the irregularities which are evident in the “smooth-edged” cusps of the upper teeth of other squaloid sharks when sufficiently magnified.

All the known male specimens of C. foliaceus are immature, as evidenced by their claspers, which are only half to two-thirds as long as the posterior inner margin of the pelvic fin in the 351 mm specimen from Japan (Bigelow and Schroeder, 1957, Fig. 7, F), the 480 mm specimen from New Zealand (Text-fig. 4, A, as C. squamosus), and the holotype of 407 mm (personal communication from Mr. A. C. Wheeler of the British Museum). The female specimens from New Zealand show little or no development of the ovaries, oviducts, or uteri. Perhaps a better indication of the immaturity, and in fact juvenile status, of the known specimens of this species, is the presence of obvious, recently-healed yolk-sac scars on all the New Zealand specimens. Such scars are also evident on two Japanese specimens of 351 mm^* but not on the holotype. However, it is reasonable to assume from the size of the latter compared to the New Zealand and Japanese examples, and the state of its claspers, that it is also a juvenile.

The presence in New Zealand waters of two “species” of Centrophorus, resembling each other closely in most features, and falling into two very distinct age-groups, one represented by the mature specimens of C. nilsoni more than 1,000 mm long, the other by the immature and juvenile specimens of C. foliaceus 400—500 mm long, with no other size-groups of either “species” known, suggests, a priori, a parent-juvenile relationship. The basis for assuming this relationship is provided, firstly by the size of the recently-born C. foliaceus—a size which demands that they grow into adults maturing at 1,000 mm or more, and hence adults the size of C. nilsoni. Secondly, comparison of the proportional dimensions of C. foliaceus (Table I, columns A, B and C) with those of C. nilsoni (columns E and F) shows striking agreement between them. Of the differences in dimensions that do occur, particularly between the smallest specimens of C. foliaceus and the two specimens of C. nilsoni, many can be disregarded when the range of variation shown for the same feature by the five New Zealand specimens of C. foliaceus is taken into account. Thus the length of base of the 1st dorsal fin is 6.6% in the holotype of C. foliaceus and 9.8% in the holotype of C. nilsoni, a difference that would appear significant. But in the five New Zealand specimens of C. foliaceus, all somewhat larger than the holotype, the range for this feature is 7.3% to 8.2%, thus bridging the gap. The same holds true for the apparent discrepancies in the distance from the snout to the gill-openings, and for other proportions too. However, not all the differences

Text-fig. 1.—Figs. A–D, pectoral fin outlines of some species of Centrophorus. Fig. A—C. foliaceus, male 497 mm, New Zealand; Fig. B—C. acus, holotype, male 819 mm, Japan (after Bigelow and Schroeder, 1957, Fig. 8, D); Fig. C—C. squamosus, female 1,230 mm, Iceland (after Bigelow and Schroeder, 1957, Fig. 8, B); Fig. D—C. nilsoni, female 1,370 mm, New Zealand.

Figs. E–G—Dermal denticles from some species of Centrophorus. Fig. E—C. foliaceus, male 480 mm, New Zealand. Fig. F—C. acus, holotype, male 819 mm, Japan (after Garman, 1913, Pl. 12, Fig. 8). Fig. G—C. nilsoni, female 1,370 mm, New Zealand.

Fig. H—A group of dermal denticles from high on the side of a female specimen of C. foliaceus, 515 mm, from New Zealand, showing four larger and wider newly-erupted denticles, and four smaller and older denticles.

can be explained in this way, as for example in the case of the distance from origin to origin of the pectoral and pelvic, these being 36.2% and 44.8% of the total lengths of the holotypes of C. foliaceus and C. nilsoni respectively. Allowing for the variation in this feature of the New Zealand specimens of C. foliaceus (33.0% to 37.4%) and the two specimens of C. nilsoni (41.1% to 44.8%), a difference of about 4% still remains. It seems not unreasonable to attribute this, at least in part, to variation with growth of the species, about which little is known for elasmo-branchs in general other than that it does occur.

If the above assumptions on the meaning of the differences between the dimensions of C. foliaceus and C. nilsoni are correct, any basis for separating these species must depend on morphological detail. In this respect, various characters have been put forward. Fowler (1941, p. 229) separates C. nilsoni from C. foliaceus

because in the holotype of the former the 1st dorsal fin is slightly higher than the 2nd. But in the second specimen of C. nilsoni the reverse is true, and hence in agreement with the usual condition in C. foliaceus Bigelow and Schroeder (1957, p. 83) distinguish C. nilsoni from C. foliaceus because firstly the posterior pectoral corners are extended in C. nilsoni but quadrate in C. foliaceus; and secondly because the fin spines of C. nilsoni are low and largely covered, whereas those of C. foliaceus are long and well-exposed. The New Zealand specimens of C. foliaceus show much greater variation in the length of the pectoral extension than was formerly known for this species, so that although the specimen of C. foliaceus on which Bigelow and Schioeder based their key characters had quadrate posterior pectoral angles as do also some of the New Zealand specimens, others have pectoral extensions of 1/20th the length of the fin. The difference between C. nilsoni and C. foliaceus is, then, at the least, the difference between extensions 1/12th and 1/20th the lengths of the fins respectively (Text-fig. 1, A and D), a difference which can hardly be sustained as a key character when allowance is made for possible variation with growth.

The fin spines of C. nilsoni emerge from the anterior margins of the dorsal fins at about the same height from the bases of the fins as do those of C. foliaceus. Their bases are, then, covered to the same extent with integument as those of C. foliaceus. As stated above, the spines of C. nilsoni appear worn or eroded; if this is the case, then the reduction in their extremities would give them the appearance of being “low and largely covered”, as described by Thompson (1930, p. 277) and used as a key character by Bigelow and Schroeder.

The only other character by which C. foliaceus can be separated from C. nilsoni is the nature of the dermal denticles. Those of C. foliaceus are long, blade-like and tridentate, with a high median ridge, and rise steeply from the skin (Text-fig, 1, E; Text-fig. 5, A—E, as C. squamosus); while those of C. nilsoni have subovoid blades, with a shorter medium tooth, several inconspicuous lateral teeth, and lie along the skin rather than away from it (Text-fig. 1, G; Text-fig. 3, A—D, K, as C. squamosus). The difference between these two types of denticles are considerable, but in view of what is now known of denticle changes with growth in species of other squaloid genera, particularly in the genus Centroscymnus (described in detail for C. coelolepis in Bigelow and Schroeder, 1954, p. 47), they cannot be accepted without question as criteria for specific distinction. Certainly the denticles of C. foliaceus resemble those of the juveniles ofCentroscymnus spp. in which denticle changes do occur— in other words such juvenile denticles share common characteristics of being markedly tridentate, with a very long median tooth half or more of the total length of the blade; with considerably shorter lateral teeth, and with the blades rising steeply from the skin as is the case in the juvenile of Centroscymnus waitei (see Garrick, 1955, Text-fig. 2D). Direct evidence is available, however, that denticle changes do, in fact, occur in C. foliaceus. Examination of the largest of the New Zealand specimens of C. foliaceus, a female 515 mm long, shows that although the majority of the denticles on the flank below the first dorsal are like those of the smaller specimens and of the holotype, there are, scattered throughout them, newly erupted denticles, not yet pigmented, rising less steeply from the skin, and of a different shape (Text-fig. 1, H). These new denticles are larger, wider in proportion to their length, and have a shorter median tooth. Most of them are tridentate, but some have two or three iiregular lateral teeth on each side, and thus show some approach to the type of denticle found in C. nilsoni. In Centroscymnus coelolepis, the final generation of denticles appears on specimens slightly more than half-grown; if the same applies to C. foliaceus, it could be expected that only on specimens 700—800 mm long or longer would adult type denticles be found. As the largest known specimen of C. foliaceus is only 515 mm, it cannot be expected to show adult type denticles. From a slightly different viewpoint, the absence of adult specimens

with “foliaceus” type denticles, though at least 12 juvenile specimens are known from a wide range of depths, in itself appears significant, and suggests that adult “foliaceus” type denticles are non-existent, presumably through their replacement by denticles of another type.

On the basis of this evidence, the separation of C. nilsoni from C. foliaceus is not justified. Accordingly they are regaided here as one species for which the name C. foliaceus would have priority.

Comparison of C. foliaceus as recognised above, with other species of Centrophorus shows that further integration is possible. The genus Centrophorus includes three species groups, well characterised by the nature of their denticles, which may be block-like, scale-like or conical. The group with scale-like denticles, to which C. foliaceus belongs, includes, as recognised currently by Bigelow and Schroeder (1957) in their masterly review of the Squaloidea, only two other species These are C. squamosus (Bonnaterre) 1788, from the eastern North Atlantic, and C. acus Garman, 1906, from Japan. Both of these species closely resemble C. foliaceus in their overall morphology. In fact, their proportional dimensions, as shown in Table I, columns G and D, give no reason for their separation.

The apparent distinction of C. squamosus from C. foliaceus because its first dorsal base measured from the origin of the spine is about twice as long as that of the second when similarly measured (as illustrated in Jensen (1899, Pl. III, A) and used as a key character by Bigelow, Schroeder and Springer (1953, p. 225)) cannot be sustained, for in a 1,250 mm specimen of C. squamosus (Mus. Comp. Zool. No. 37825) from Iceland the lengths of the dorsal bases are 9 8% and 7 8% of the total length respectively, and thus well in accord with those of C. foliaceus (personal communication from W. C. Schroeder).

The posterior corner of the pectoral fin of C. squamosus (Text-fig. 1, C) has about the same degree of extension as that of adults of C. foliaceus (Text-fig. 1, D, as C. nilsoni) And the excellent illustrations of the teeth and denticles of C. squamosus in Jensen (1899, Pl. III, B—R) agree so closely in their details with those of the New Zealand adults of C. foliaceus (Text-fig. 2, E—H, Text-fig. 3., A—K, as C squamosus) that there can be no question of distinction in these features.

There is, then, no reason for separating C. foliaceus from C. squamosus, the latter name having priority This makes C squamosus a bipolar species, and parallels the case of Centroscymnus crepidater Bocage and Capello, 1864, previously known only from the North Atlantic, but recently recorded from New Zealand (Bigelow and Schroeder, 1957, p 93).

The relationship between C. squamosus as recognised above and C. acus is not as clear cut. Their proportional dimensions agree closely (Table I), as do the lengths of their pectoral fin extensions, or the details of their teeth. However, the denticles of the holotype of C. acus, as illustrated in Garman (1913, Pl. 12, Fig. 8) and Bigelow and Schroeder (1957, Fig. 11D) differ markedly from those of either juveniles or adults of C. squamosus, but they have a close resemblance at least in outline to the few newly-erupted denticles in the New Zealand specimen of 515 mm now regarded as C. squamosus (cf. Text-fig. 1, F, with 1, H). If C. acus does represent a growth stage of C squamosus, then the denticles on a specimen the size of the holotype (819 mm long) would, on the assumptions made above, approximate to those of adults of C. squamosus, that they resemble, in outline, the denticles of more juvenile specimens may mean that C squamosus undergoes denticle changes at a later stage than specimens of Centroscymnus coclolepis. Alternatively, it may indicate that C. acus is a distinct species.

Bigelow and Schroeder (1957, p. 78) further separate C. acus from C. foliaceus on the grounds that the denticles of C. acus are less regularly overlapping, and relatively smaller. Little reliance can now be placed on the first of these characters because of its varrability with growth The denticles of the holotype of C. foliaceus

Text-fig. 3.—Centrophorus squamosus, male 1,030 mm (holotype of C. nilsoni), New Zealand Figs. A–G—Dermal denticles from high on side at level of 1st dorsal fin Fig. A—external view showing arrangement of denticles. Fig. B—External view of denticle showing underlying base Fig. C—Lateral view. Fig. D—Apical view. Figs. E—G—Outlines of denticle bases, showing variation in the scalloping of the anterior margins, and the major and minor ridges. Fig. H—Denticle from caudal fin. Fig. I—Denticle from 0.5 cm posterior to lower lip. Fig. J—Denticle from margin of lower lip. Fig. K—C. squamosus, female 1,370 mm, New Zealand: dermal denticle from high on side at level of 1st dorsal.

(407 mm long) are more overlapping than those of any of the New Zealand specimens. including the smallest (438 mm), originally ascribed to this species. Presumably the greater spacing of the denticles on these slightly larger specimens is due to growth of the trunk separating the individual denticles of the first generation. Succeeding generations of denticles, the first of which are appearing in the 515 mm specimen, would close the gaps so produced.

Whether the smaller relative size of the denticles of C. acus is significant must remain unanswered until further specimens of this species are available; other evidence suggests that it may, in fact, reflect specific distinction. Although the denticles of C. acus have the same shape as the newly-erupted denticles in the 515 mm specimen of C. squamosus from New Zealand, they differ in other features. The median longitudinal ridge on the blade of each denticle of C. acus is “relatively feeble” (personal communication from W. C. Schroeder who has compared the denticles of the second adult specimen of C. squamosus from New Zealand with those of C. acus); this contrasts strongly with C. squamosus, where the median ridge is very high, not only in adult denticles, but also in those of juveniles. And as well, the pedicles of the denticles of C. acus are wider, in lateral view, than are those of C squamosus Other differences between C. acus and C. squamosus are the shape of the pectoral fins, the distal margins of which slope posteroventrally in C. acus when the fin is adpressed to the trunk, whereas those of C. squamosus are almost vertical (cf. Text-fig. 1, B, with A, C and D); and the less tapered snout contour of C. acus, as shown in the illustrations of the holotype (Garman, 1913, Pl. 12, Fig. 7).

C. acus is therefore considered as distinct, though further specimens may show