OF CONCHOLOGY. 185 



diiferent figures, and yet the character of the ellipse allows of an 

 immense variation, so that one form of it may be superficially 

 entirely unlike another, and only distinguishable from the circle 

 by exact measurement. And yet the circle-like ellipse has all 

 the elements of the ellipse. 



As it might be supposed that such diiferences as those cited 

 must be so obvious as to have at once been remarked, and that 

 there was universal tacit acquiescence as to the fact, but con- 

 tempt of the systematic value, it may be added that, in the latest 

 edition of the most esteemed " Manual of the Mollusca," Am- 

 phiperas or '■'■Ovulum, Lam.," is expressly defined as having a 

 "shell like Cyprcea ; inner lip smooth," and that both the latter 

 and the family Cyprseidse are accredited with a " spire con- 

 cealed." In the latest monograph of the family, the shell is ex- 

 pressly said to have a "spire more or less immersed, mostly [!] 

 concealed," and it is remarked that "Linnaeus is not to be com- 

 plimented on his sagacity in having referred the typical species 

 of this group to Biilla. The resemblance of the shell of Ovu- 

 lum to that of Cyprcea is obvious enough, and there is a simihir 

 affinitj' between the animals of the two genera. The Ovidum 

 is, in fact, a Cowry, with the extremities more or less pro- 

 duced."* 



It may, however, be justly regarded as rather meritorious on 

 the part of Linne to have remarked that real similarity of de- 

 velopment of the shells of the formis now called Amphiperasidse 

 and Bullidse which induced him to place them in one genus; he 

 at least did not assign a spire to shells in which it is entirely ab- 

 sent : as to his reference of the species to Bulla, it is more than 

 possible that he really regarded the Amphiperasidae as the typi- 

 cal species of Bulla, but, as he mentioned no type, it seems ex- 

 pedient to recognize the subsequent subdivision of that group, 

 and the limitation by exclusion to the restricted genus now uni- 

 versally recognized under the name Bulla. 



Lest the previous remarks may be misunderstood, it may, 

 however, be added that the similarity noticed is simply analogi- 

 cal ; for, however similar some of the shells of the respective 

 families may be {i. e. Volvula and Atys, and most of the Am- 

 phiperasidse), the study of the entire organization demonstrates 

 that they belong to two different subclasses of the Mollusca. 



The neglect to notice the true character of the shell of Am- 

 phiperas is the more remarkable, as in the classic work on the 



* Reeve, Monograph of the geaus Ovulum, 1865, Diagnosis and 

 Remarks. 



