OP CONCHOLOGY. 



183 



ON THE RELATIONS OP THE AMPHIPERASIDiE. 



BY THEODORE GILL, M. D., PH. D. 



Various species and groups of species, -which a critical exami- 

 nation demonstrates to be little related to each other and indeed 

 to be very widely removed from their mimetic analogues, are yet 

 so simihar in superficial form or features, that close approxima- 

 tion of such is perfectly justifiable and may perhaps be the only 

 alternative so long as the entire organization rcnmins unknown. 

 Numerous are the molluscous forms that have been thus approx- 

 imated on account of a similarity of the shells, but which are 

 now ascertained to belong to entirely different groups. Refer- 

 ence need only be here made to the patelliform shells, now dis- 

 tributed among different orders and subclasses, to Lunatia and 

 Ampullaria, to Meladonius and Viviparus, to 3Iarisa and Pla- 

 norbince, to Erato and the 31arginellidce, to Turridce and the 

 Mitridce,* and to the A7nj)Idperasidce and Cyprceidce. But it must 

 be confessed that while the similarity between most of the groups 

 just contrasted is very considerable, that between the Araphipe- 

 rasidae and CypriTeidie is in truth comparatively sliglit and of the 

 most superficial nature. And yet the distinctness and the re- 

 mote character of the affinities of the really similar shells is now 

 generally admitted, while many of the best conchologists still 

 approximate next to each other, and evidently with the idea 

 that their affinity is more than usually great, the last mentioned 

 groups. It will therefore not be a labor of supererogation to 

 inquire into the propriety of such a collocation. 



It is evident that the idea of the affinity of the Amphipera- 

 sidse and Cyprseidge has been insensibly, perhaps almost wholly, 

 derived from the largest and one of the most common and well 

 known species — the Ampliiperas ovum. And certainly there is 

 considerable similarity in the general contour of that species to 

 that of the Cyprseidae, and even in color there is a likeness to 



* Dr. Troschel has overlooked the prior foundation, by J. E. Gray, of 

 a family [Turritidce) based on the same characters as Strigatellacea. See 

 Gray, Proc. Zool. Soc. ; Guide, 1857, p. 23. 



