186 AMERICAN JOURNAL 



Mollusca it was especially described,* and the genus was ex- 

 pressly distinguished from Cyproea by the constant absence of 

 the spire. f It is true that Lamarck failed to appreciate the 

 value of the diflf'erence he perceived, but it must be remembered 

 that the relations of analogy and affinity were not then so well 

 understood as now, and he, too, was unduly impressed by the 

 similarity of contour between the two groups. 



The impression conveyed by the superficial resemblance of 

 the shells has been carried over to the consideration of the ani- 

 mal, and formerh"^ the belief was current tliat the animals of the 

 two groups were scarcely distinguishable, or, as M. Desliayes has 

 remarked, zoologists were not surprised to find that between the 

 two tliere was a perfect identity .% M. Desha3^es himself has, 

 however, while convinced of the justice of M. de Blainville's 

 opinion, discovered differences between the two forms — not, how- 

 ever, the important ones now recognized — although he has re- 

 garded them as of slight value. But when it is asserted that 

 there is a complete identity between the two, or that the differ- 

 ences are slight, it can only be because the two forms exhibit 

 the normal gasteropodous structure with adaptive modifications 

 as regards the shell, and with no very prominent special exter- 

 nal modificjitions; for a more profound study of the organiza- 

 ition reveals the most important dilferences. In the first place, 

 the Amphiperasidge have a non-retractile snout or muzzle, while 

 the Cyprgeidae are one of a small group provided with a snout 

 retractile from the tip. Other important differences in the struc- 

 ture of the or:il region have been observed,! and the dif- 

 ference in the dentition of the radula is very marked, the late- 

 ral teeth having an unsymmotrical fan-like form, expanding 

 .towards their extremities and finely pectinate. It must also not 

 be forgotten that the visceral sack is the mould on which the 

 shell is framed, and that there must be corresponding differences 

 -between it and that of the Cyprseidae. 



In view of tlic differences observed by him. Dr. Troschel has 



* " Ellea 8ont enroulees sur ellesmemes de maniere que leur cavite 

 tounie autour de I'axe de la coquille et Teuveloppe entierement, en sorte 

 qu'elles n'ont reellement poiut de spire." Lamarck, H. N. des Animaux 

 8. Vert., 2e ed. x, p. 465. 



t " Ce caractere du bord gauche jamais dente, et celui d'uu defaut 

 constant de spire, suffisent })our distinguer les Ouules des Porcelaines." 



t " Aussi, hirsque M M. Quoy et (Jaimard * * * eurent rapporte 

 I'animal de 1' Ouida oviformis, et lorsque M. de Blainville en eut donne 

 une description et une figure, les zoologistes ne furent point etonnes de 

 trouver, entre cet animal et celui des Porcellaines, uue identite com- 

 plete." Deshayes in Lamarck, \\. N. des Animaux s. Vert., x, 1844, 

 p. 465. 



§ See Troschel, Gebiss der Schnecken, i, p. 216, 217, 



