CALYPTil^A. 



proach each other so nearly, that we had hesitated td 

 separate them; the principal differences consist in the 

 apex of Crepidula being lateral or nearly so, and in the 

 internal appendage forming a nearly straight septum 

 across the aperture, hut it is rather difficult to say at f 

 which particular species Calyptraea should end, and Crepi- 

 dula should begin. With respect to its place in the sys- 

 tem, we are disposed rather to accord with Cxivier in 

 considering it as more nearly related to the Sigareti and 

 Buccina, than with Lamarck in placing it near the Pa- 

 tellfje, or in supposing that, here the spiral shells With 

 an entire aperture commence and form a particular series 

 as a lateral branch/' 



Shell generally in the form of a more or less obtuse 

 cone, with a nearly central, imperforate vertex, and the 

 base more or less regularly orbicular, entire and sharp- 

 edged. Cavity inferior, furnished with a lateral, internal 

 appendage, very variable in form: in some species, as 

 for instance C. deformis, (a fossil from Bordeaux) this 

 appendage is only a small irregularly triangular piece 

 attached by its longest side to the inside of the shell; in 

 these the inner lip may be considered as reflected at its 

 upper part upon itself, without forming an umbilicus; in 

 others the appendage taking its rise, and being fixed only 

 near the summit, forms a kind of tongue increasing in 

 width, and having both its edges turned towards the mid- 

 dle of the shell : in others again, this appendage forms a 

 more or less distinct cup, the inside of which is analo^ 

 gous to the umbilicus in other shells, and it is formed by 

 the reflection of the upper part of the inner lip without 

 its being at the same time depressed upon itself : in a 

 fourth division of this Genus, which most nearly ap- 

 proaches the CrepidulcB, this appendage is a spiral plate, 

 reflected at the upper part so as to form a small umbilicus. 

 In many species a strongly marked muscular impression 

 is observable just above the fold of the inner lip; in 

 others it is placed upon the appendage, or outside the 

 inner cup itself, but never within the umbilicus, or inner 

 cup: in those which have a single triangular laminar 

 appendage, it is partly placed on it and partly above it. 

 These shells are generally thin; though sometimes re- 

 markably thickened by circumstances attending their | 

 growth. The outside is often smooth^ more frequently \ 



