BY H. L. KESTEVEN. 77 



from the following statement: — "The protoconch and 

 nepionic shell in the Tritons are practically continuous and 

 inseparable. . • . The nuclei of the Australian fossil forms, 

 as figured by Kesteven (27), indicate that a protoconch, as' 

 distinguished from the nepionic shell, was present in some if 

 not all these forms." From this it follows that his interpre- 

 tation of the term Neanic is the same as mine ; he applies it 

 to the early whorls of the true conch. 



Dr. Ball's justification for the segregation of these species 

 from the rest of the genus rests upon their supposed posses- 

 sion of three characteristics, viz. : — 



1. "Sejita is separated from the other Tritons by its later- 

 ally extended rachidian tooth with a median inflexion in 

 front, but without basal plates, recalling that of Cassis." 



2. "The operculum of Septa has it (the nucleus) subcen- 

 tral and internal." 



3- "In one group alone. Septa, is there a distinctly marked 

 neanic stage." "The larval shell of Septa is identical in 

 general characters (with those of other members), but is fol- 

 lowed by a neanic stage in which the elegant granular sculp- 

 ture, and delicate rose colour of the test contrast effectively 

 with the features of the adult, though there is no very pro- 

 nounced line of demarcation between the two." 



A generic segregation, or in fact any segregation, of a 

 group of species can be justified only on one or both of two 

 grounds. The features relied upon for the segregation must 

 be either of Phylogenetic significance, or else they must be of 

 such a kind as to minister to the convenience of the Taxono- 

 mist, and the science generally through a more or less artificial 

 classification. 



Only one of the above features has any real claim to be 

 regarded as of phylogenetic significance, namely the charac- 

 ter of the radula ; the value of this, as of most other charac- 

 ters for taxonomic purposes, is to a certain extent determined 

 by the personal factor, but I would point out that the differ- 

 ences between the radulae of G'i/mafiu?n cutaceum Linn., and 



