GASTEROPODA. 149 



upon the shell most distinctly on both sides of the aperture, and I have presumed 

 fig. 9, /, to have been the operculum. 



Natica depkessula. — Some small specimens in my cabinet, not more than a 

 line in diameter, passed under this name in my Catalogue. They are depressed in 

 the volution with a deep and distinct suture, that does not appear to have been 

 produced by erosion, and differ in that respect from the young of some well-deter- 

 mined species that I have traced downwards to no greater magnitude. They must, 

 however, for the present, be considered of doubtful character. 



Sigaretus, Jdanson, 1757. 

 Stomatia. Browne. 1756 (fide Gray). 

 Cryptostoma. Be Blainv. 1825. 



Gen. Char. Shell auriform, or ear-shaped, suborbicular, oblique, with a depressed 

 spire, and consisting of few and rapidly increasing volutions, striated or reticulated 

 upon the exterior ; aperture much dilated, wider than long ; peritreme disconnected 

 by the body whorl, with, generally, a small but open umbilicus, and a thin corneous 

 operculum. 



The shells of this genus are said to be entirely enveloped by the mantle of the 

 animal, although the exterior is covered with striae or reticulations. It is dis- 

 tinguished from Stomatia, Lamarck, by the texture of the shell, which in this is not 

 nacreous, and from M'trsenia, to wiped it approaches nearer in form, by its thicker 

 and more opaque shell, and by its having the inner lip spread over the body whorl, 

 forming an umbilicus, in Morsenia the left side is sharp and truncated, visible 

 internally up to the spire. 



All the known recent species of this genus are natives of warm climates, and 

 two or three species have been found in the Eocene formations. It is first quoted 

 from the Devonian period. 



1. Sigaretus excavatus. S. Wood. Tab. XV, fig. 11. 



S. Tesfd minuld, auriformi, tenui. fragili ; spird act/Id, prominuld ; anfrac/ibus tribus, 

 depressis, obUquis, supra convexis, mbiw planatis, imbricatis ; ad marginem obtuse angu- 

 lalis, Iransoersim undulaio-striatis, striis exihssiinis ; aperiurd patent e ; v/mbil/ico magno, 

 profundo. 



Shell small, thin, and fragile, with a slightly prominent spire, and acute apex; 

 composed of three depressed volutions, convex on the upper part, and flat beneath, 



