Summary

• (i) Centrophorus plunketi Waite, 1910, has pectoral fins with rounded posterior corners; upper teeth which are noticeably longer midway out along each side of the jaw than at the centre of the mouth; and ovoid tridentate dermal denticles which carry strong median longitudinal ridges extending the full length of the blades. On these characters, the species is referred to Scymnodon.

• (ii) The lower teeth of S. plunketi are like those of Centroscymnus spp.—i.e., all oblique and without a symmetrical median tooth; but they are not of generic significance. In S. plunketi they have specific value in that they separate it from all other species of Scymnodon (in which the lower teeth are erect at the centre of the mouth, and there is a symmetrical median tooth).

• (iii) Centroscymnus waitei (Thompson, 1930), based on a juvenile specimen, is a young stage of S. plunketi. Juveniles of S. plunketi have dermal denticles with concave ridgeless blades which differ markedly from the strongly ridged blades of adult denticles. Intermediate form denticles have a shallow median longitudinal ridge, and first appear on the caudal peduncle of juveniles about 500 mm long. This is the first record of changes in dermal denticle form in Scymnodon, and is novel in that ridgeless denticles are replaced by ridged ones.

• (iv) New Zealand catches of S. plunketi are from 120–780 fathoms, which approximates the full range of the species It is abundant in 300 fathoms and deeper. It is probable that it is a schooling species, at least on occasions, segregating