186 AMERICAN JOURNAL 



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

 pressly distinguished from Cyprcea by the constant absence of 

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

 value of the difference 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 formerly the belief was current that the animals of the 

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

 remarked, zoologists were not surprised to find that between the 

 two there was a perfect identity.X M. Deshayes 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 modifications; for a more profound study of the organiza- 

 tion reveals the most important differences. In the first place, 

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

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

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

 ture of the oral region have been observed, § and the dif- 

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

 ral teeth having an unsymmetrical 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 Cyprgeidae. 



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



* " Elles sont enroulees sur elles-niemes de manie.re que leur cavite 

 tourne autour de I'axe de la coquille et I'enveloppe eiitierement, en sorte 

 qu'elles n'ont reellenietit point 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'un defaut 

 constant de spire, suffisent pour distinguer les Ovules des Porcelaines." 



J " AUiSsi, lorsque MM. Quoy et Gainiard * * * eurent rapporte 

 I'animal de 1' Ovuta 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 Porcellainea, une identite com- 

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

 p. 465. 



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



