264 MOLLUSCA. 



interposes itself between a fold of the abdominal sac. The branchiae are 

 composed of a range of numerous filaments, long and slender, like hairs. 



SiPiiONARiA, Sowerby. 

 The shell of the Siphonarise, which have been recently separated from the 

 Patellae, at the first glance seems very similar to a flattened Patella, with 

 radiating sulci; but its margin projects ratlier more on the right side, and it 

 is excavated beneath by a slight furrow, which terminates at this promi- 

 nence of the margin, to which there is a corresponding lateral hole in the 

 mantle, for the introduction of water into the branchial cavity, placed on 

 the back, that is closed on every other point. The respiratory organ con- 

 sists of a few small lamellse, arranged in one transverse line on the roof of 

 that cavity; the tentacula seem to be wanting, the head being merely fur- 

 lushed with a narrow veil. 



SiGARETus, Adans. 

 The shell is flattened, its aperture ample and round, and the spire very 

 moderate, its whorls rapidly enlarging and seen within, but concealed dur- 

 ing the life of the animal in the thickness of a fungous shield, which projects 

 considerably beyond it, as well as tlie foot, and which is the true mantle. 

 Before this mantle are an emargination and a semi-canal, which serves to 

 conduct water into the branchial cavity, and which form the passage to the 

 following family, but of which there are no impressions on the shell. The 

 tentacula are conical, with the eyes at their external base. 



Cryptostoma, Blainv. 

 The shell, resembling that of a Sigaretus, with the head and abdomen, 

 which it covers, supported by a foot four times its size, cut square behind, 

 and forming before a fleshy, oblong bundle that constitutes nearly one half 

 of its mass. The animal has a flat head, two tentacula and a broad bran- 

 chial comb on the roof of its dorsal cavity. 



FAMILY III. 



BUCCINOIDA. 



This family has a spiral shell, in the aperture of which, near the • 

 extremity of the columella, is an emargination or a canal for trans- 

 mitting the siphon or tube, whicli is itself but an elongated fold of 

 the mantle. The greater or less lengtli of the canal, when there is 

 one, the size of the aperture, and the form of the columella, furnish 

 the grounds of its division into genera, which may be variously 

 grouped. 



