64 Transactions. — Zoology. 



Genus Onithochiton, Gray (1847). 



0. undulakis, Guoy and Gaimard. 

 Man. N.Z. Moll., p. 114. 

 Lineolata, Hutton (not of Frembly), is a synonym. 



Art. VII. — Revision of the Neio Zealand Pleurotomidae, 

 ivith Descriptions of Six New Species. 



By Henry Suter. 



[Read before the Philosopliical Institute of Canterbury, 2nd November, 



1898.] 



Plate III. 



The diagnosis of the family is given by Tryon'-' as follows : 

 " Shell fusiform, with a more or less produced anterior canal, 

 and a slit or sinus of the outer margin of the aperture near 

 the suture. Operculum (not always present) corneous, 

 annular, the nucleus apical, or subcentral, or nearly marginal. 

 The dentition is usually 1 — — 1, but in some groups there is 

 a rhachidian tooth, and in others there are two laterals. No 

 jaws." 



With regard to making a satisfactory classification, it may 

 not be out of place to quote a few of Tryon's remarks on the 

 subjectf : " In no other group of Mollusca is it so difficult to 

 make a satisfactory classification. Many species are very 

 variable in their characters, whilst the material for the 

 recognition of most of those described is generally scanty. 

 The many generic and subgeneric groups that have been 

 made only increase the confusion, for so great is the varia- 

 bility of all the characters that nearly allied species have 

 been constantly separated into different groups." 



As the dentition and operculum of most of the New Zea- 

 land species are unknown, the present classification rests on 

 the characters of the shells alone, and is therefore open to 

 amendment. 



The deep-sea species hardly form part of the New Zealand 

 fauna, but I include them here, as some of them may be found 

 inhabiting our shores in lesser depths. 



* Trjon, Man. Conch. (1), vol. vi., p. 151. 

 t I.e., pp. 151, 152. 



