OP CONCHOLOGY. 



183 



ON THS RELATIONS OF THB 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 '".videly removed from their mimetic analogues, are yet 

 so similar 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 remains 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 

 AmiJullaria, to Meladomus and Viviparus, to Marisa and Pla- 

 norhince, to Erato and the Marginellidce, to Turridce and the 

 dfitridce,* and to the Ampliiperasidce and Cyproeidoe. But it must 

 be confessed that while the similarity between most of the groups 

 just contrasted is very considerable, that between the Ayiphipe- 

 rasidae and Cyprseidre is in truth comparatively slight and of the 

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

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

 generally admitted, while many of the best conchologists siill 

 approximate next to each other, and evidently with the idea 

 that tlieir aflBnity 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 afiinity of the Amphi[)era- 

 sidae and Cyprseidae has been insensibly, perhaps almost wholly,, 

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

 known species — the Ainphiperas ovum. And certainly there is 

 considerable similarity in the general contour of that species to 

 that of the Cyprgeidae, 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. 



