along the whole jaw, and there is no symmetrical median tooth (Text-fig. 2). In these lower teeth characters it corresponds with the condition in Centroscymnus. However, as has already been shown by Garrick (in press) the lower teeth are not always reliable criteria even in Centroscymnus, and where there is confusion from reference to the upper and lower teeth this can be resolved in all except the most juvenile specimens by examination of the dermal denticles. On the Plunket shark these are ovoid, tridentate, and have a median longitudinal ridge extending along the entire length of the blade (Text fig. 3), leaving no doubt that the species is referable to Scymnodon. Such denticles contrast with those of Centroscymnus which are more circular in outline, have an uninterrupted circular concavity at the anterior end, and when a median longitudinal ridge is present, it is restricted to the posterior half or two-thirds of the blade, behind the concavity.

Although the obliqueness of the lower teeth of S. plunketi is without generic significance, it does set this species clearly apart from the three other species of Scymnodon currently recognised. In this respect it is as unusual a feature as the transverse ridging which occurs in addition to the usual longitudinal ridging on the dermal denticles of S. obscurus (Vaillant, 1888), but is not found on those of S. ringens Bocage and Capello, 1864, or S. squamulosus (Gunther, 1877), (or, for that matter, S. plunketi).

Compared with S. ringens (figured in Bigelow & Schroeder, 1957, Fig. 13, A-E) and S. squamulosus (in Gunther, 1887, Pl. 2, Fig B), S. plunketi more resembles S. ringens in its overall heavy-bodied form and short snout. However, it differs from S. ringens in having a well-marked concavity in the lower posterior margin of the caudal fin; the posterior tip of the second dorsal fin reaching only as far back as the level of the hypural origin; shorter gill-openings; and in a much greater interspace between the tip of pectoral fin, when laid back, and the level of origin of the 1st dorsal spine (almost equal to the interspace between the eye and the first gill-opening in adult specimens, though much shorter than this in juveniles).

Differences between S. plunketi and S. squamulosus include a much blunter and shorter snout in the former (the preoral length noticeably less than the width of the mouth in S. plunketi, but much more than this width in S. squamulosus); and much larger first dorsal and pectoral fins in S. plunketi which by comparison make those of S. squamulosus appear markedly slender.

It was suggested by Thompson (1930, p. 278) that the species he described as Centrophorus waitei from a single juvenile specimen taken in deep water off Kaikoura might prove to be a growth stage of S. plunketi. This view has not been accepted completely by later authors mainly because the dermal denticles are markedly different Waite (1914) had previously described late embryos of S. plunketi, which Thompson does not mention having available for comparison, and they cannot now be found in the Canterbury Museum. Direct comparison of Thompson's specimen with Waite's identified embryos of S. plunketi is therefore not possible, and no other embryos or juveniles of the latter species have been described. As a consequence Thompson's species has been retained, though Whitley (1940, p. 143) referred it to Proscymnodon, but later (1956, p. 398), following Garrick (1955) to Centroscymnus. Bigelow and Schroeder (1948, p. 451, footnote 8) considered it to be a Scymnodon, but later (1957, pp. 88–96) also transfer it to Centroscymnus and reaffirm Thompson's suggestion that it may be a young stage of S. plunketi. Garrick (1955) gave a full description and illustration of the type of C. waitei, and, chiefly on the nature of the dermal denticles which have strongly concave blades and lack longitudinal ridges, regarded it as a Centroscymnus.

Since Garrick's (1955) study, further juvenile specimens seemingly C. waitei, have become available. These include two male embryos in the Dominion Museum collections, 336 and 348 mm long (Dom. Mus. No. 763) labelled “C. plunketi”,

from Cook Strait, 1929; and one female 523 mm long (Dom. Mus. No. 2637) long-lined from 500 fathoms off Kaikoura by Mr. R. Baxter in November, 1955. These all agree closely with the type of C. waitei except that their caudal fins have a more or less truncate terminal lobe and a definite subterminal notch (Text-fig. 1, A). In this respect they resemble other species of Centroscymnus and Scymnodon, and hence the unusually pointed caudal fin of the type of C. waitei can no longer be regarded as a distinctive feature of this species. The proportional dimensions of the 523 mm specimen are more or less intermediate between those of the type of C. waitei (318 mm) and those of two adult specimens of C. plunketi (1197 mm and 1417 mm), as in Table I, so that no specific distinction is apparent. Such variation as is present can be recognised as change with growth, the adults having proportionately longer bodies, and shorter heads and tails relative to the juveniles. Equivalent variation has been reported for species of Centrophorus and Centroscymnus (Garrick, 1959; in press).

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The distinction between the dermal denticles of the juvenile C. waitei and those of adult S. plunketi is very misleading. The usual practice of examining denticles from the anterior half of the trunk when applied to the 523 mm specimen is equally misleading, for the majority of the denticles in this region are as in the type of C. waitei—i.e., they are well spaced, with strongly tridentate, concave, ridgeless blades rising steeply from the skin. But examination of the posterior half of the trunk shows in addition slightly larger denticles of another form which are newly erupted,^* and have a shallow median longitudinal ridge extending along the whole length of the blade (Text fig. 1, B). The presence of this complete median ridge means that the denticles cannot be those of a Centroscymnus but instead are referable to Scymnodon. Moreover, their shape and sculpture is such that they could reasonably be regarded as intermediate to the final form of the ovoid, tridentate, ridged blades of S. plunketi (Text-fig. 1, C-E).

The above leaves no grounds on which to maintain C. waitei as separate from S. plunketi. If further confirmation is required, it is provided by the teeth. The upper teeth of C. waitei are like those of other species of Scymnodon, including S. plunketi, in that they are longest midway out along each side of the jaw; but the lower teeth series share with S. plunketi the peculiar feature of being oblique at the centre of the mouth and lacking a symmetrical median tooth.

The dermal denticle changes noted above (Text-fig. 1, C-E) are the first to be recorded from a species of Scymnodon, although equally remarkable changes are known from some species of Centrophorus and Centroscymnus. However the changes in S. plunketi are novel in that no other cases are known where ridgeless juvenile denticles are replaced by ridged intermediate and adult denticles. In Centroscymnus coelolepis and C. owstonn the reverse occurs, strongly ridged juvenile and intermediate denticles being replaced by adult denticles which lack ridges or at least have them greatly reduced.

All the known New Zealand catches of S. plunketi are from Cook Strait, Karkoura and Banks Peninsula, but it is likely that line-fishing in deep-water elsewhere on our coasts would show that the species is not restricted to these areas. The depth range so far known is 120–780 fathoms and probably approximates the full range of the species, for it is rarely taken by commercial line-fishermen in 150 fathoms and shallower, and has not yet been caught on lines set deeper than 1,000 fathoms in Cook Strait. The south-eastern Australian records of the species (the only other region where it is known) give it an even narrower range of 260–450 fathoms, as shown by Cowper & Downie (1957, Fig. 12) who record 17 specimens from 7 stations, the greatest single catch of 7 specimens being long-lined in 360–400 fathoms. An indication of its abundance in 300–400 fathoms in New Zealand is shown by the catches of a commercial line-fisherman, Mr. R. Baxter, of Oaro, Kaikoura, who within a month caught sufficient specimens to yield 3,300lbs of liver. The livers average 81b to 101b per shark, so that some 300 to 400 specimens were taken within the period.

It now seems highly probable that S. plunketi is a schooling species of the deeper waters, at least on occasions, the schools segregating not only according to size but also to sex. This is shown by New Zealand catches of December, 1955, when 13 males, 1090 mm to 1198 mm long were taken in 450 fathoms, and July 1957, when 5 females 1,290 mm to 1,320 mm were caught in 600 fathoms. The Australian records also indicate that it is a bottom-dwelling species, for although it was taken there on seven occasions by the use of conventional long-lines, it was not caught at all during an extensive drop-lining programme in the same depths and region.

Text-Fig. 1—Fig. A—Centroscymnus waitei, tail of embryo male, 348 mm (Dom. Mus. No. 763). Fig. B—C. waitei, female, 523 mm (Dom. Mus. No. 2637), juvenile and intermediate dermal denticles from the flank of the caudal peduncle. Figs. C-E—Scymnodon plunketi, external views and cross-sections of the blades of juvenile, intermediate and adult denticles respectively (Figs G and D. from 523 mm female, E from 1,417 mm female), the cross-sections through a-b in each case

The New Zealand catches (where information is available) have all been from long-lines, and on the few times when drop-lines have been used in depths of 300 fathoms or more, no S. plunketi have been taken.

To date there has been no commercial exploitation of S. plunketi other than isolated catches for liver such as mentioned above. The livers have a high oil content, as shown by the analysis of a New Zealand specimen taken in December, 1956, which had 84 g. oil/100 g. fresh liver; but the vitamin A content is low, being only 370 I.U./g. oil, compared with the common figure of 30,000 I.U./g. for the School shark, Galeorhinus australis. Similar figures are given by Cowper & Downie (1957, Table VI) for an Australian specimen of S. plunketi

Cephalopod beaks and bony fish remains are the only stomach contents found in New Zealand specimens of these sharks. Of 18 specimens dissected, all of them long-lined, 12 had empty stomachs, presumably having vomited their contents. Four contained fish remains only; 1, cephalopod beaks only; and 1, both fish remains