88 CRITICAL OBSERVATIONS ON RECENT CONTRIBUTIONS, ETC. 



emploTCcl — where in each the characters depended upon by- 

 all other authorities are reduced to j^lay a subordinate part 

 in determinincj the limits of a i^'euus — so long will we be in- 

 volved in contradiction and confusion. This must certainly 

 be the case when we are assured that no single character can 

 be made to harmonise with any other character in a common 

 generic range. 



But we have still another difficulty. The local worker may- 

 zealously, as in Mr. Petterd's case, work up the hidden 

 characters of the denticulae, and show clearly the differences-, 

 so far as local examples are concerned, but if he have no ■ 

 relial)le knowledge that genera already established for similar- 

 forms of shell may or may not have corresponding dentition 

 characters, what justification is there for creating a new 

 genus for a local form of shell which in all respects corre- 

 sponds Avith one already established for this particular form, 

 irrespective of the character of its denticular? 



Take, for example, Mr. Petterd's sub-genus Bcddoincia pro- 

 posed for globosely conical shells, spire short ; body whorl 

 inflated. 



So far as apparent form of shell and animal is concerned,, 

 it answers exactly to Lithoglyphus, of Muhlfeldt, or with 

 Gillia, of Stimpson. Why, therefore, create a new genus for 

 a similar form in Tasmania. But it may be said that the 

 denticulated teeth justifies the separation. To this I reply, 

 Good. Show us proof that this is so. Have you examined 

 the denticula) of the various species of LitJwglyphus and of 

 Gillia ? If you have done so, why neglect to show the marked 

 contrast of dentition in forms extenially alike ? 



When genera are established after the fullest comparison 

 in this way few will object, but I need hardly say that 

 thrusting fresh generic names into our nomenclature is far 

 from satisfactory when the dentition of allied forms of other 

 countries have not been thoroughly examined and compared 

 with the local types. 



While it is admitted that all external and internal charac- 

 ters of the animals should be studied together, where possible, 

 few will altogether agree with Mr. Petterd's observation 

 " that in all cases the inhabitant of the shell requires thorough 

 examination before the generical position can be with certainty 

 decided." 



For, we may exclaim with Binney, "Supi)0sing the dentition 

 of all living forms to be examined (an iin])08sibility), we are 

 still confronted by the fossil shells. What shall wc do with 

 them? Shall wc use for these 30,000 species ol>vious ex- 

 ternal universal characters, yet discard these in the recent 

 mollusca for the modifications of a partial character, the very 

 slight observation of which has sufficed to show that it may 



