GASTEROPODA PECTINIBRANCHIATA. 53 



deposited with them. The figure of tliis envelope is often very 

 complex and singular*. 



Their tongue is armed with little hooks, and by slow and repeated 

 rubbing acts upon the hardest bodies. 



The greatest difference in these animals consists in the presence or 

 absence of the little canal formed by a prolongation of the edge of 

 the pulmonary cavity of the left side, and which passes through a 

 similar canal or emargination in the shell, to enable the animal to 

 breathe without leaving its shelter. There is also this distinction 

 between the genera — some of them have no operculum ; the species 

 differ from each other l)y the filaments, fringes, and other ornaments 

 of the head, foot, or mantle, , 



These MoUusca are arranged in several families according to the 

 forms of their shells, which appear to bear a constant relation to that 

 of the animal. 



FAMILY I. ' 



TROCHOIDA, 



Tliis family is known by the shell, the aperture of which is entire, 

 without an emargination or canal for a siphon of the mantle, as the 

 animal has none, and is furnished with an operculum or some organ 

 in place of itf. 



Trochls, Lin.X 



Have shells, the angular aperture of whose external border ap- 

 proaches more or less to a perfect quadrangular figure, and in an 

 oblique plane, with respect to the axis of the shell, because the 

 part of the margin next to the spire projects more than the rest. Most 

 of these animals have three filaments on each edge of the mantle, or 

 at least some appendages to the sides of the feet. 



Of those th;;t have no umbilicus, there are some in which the colu- 

 mella, that has the form of a concave arch, is continuous with the 

 external margin, witliout any projection. It is the angle and projec- 

 tion of tliis margin which distinguishes them from Turbo — Tecta- 

 rium, Montf. § 



* For :Murex, see Lister, 8S1, Baster, Op. g-abs., I, vi, 1, 2; for Bucciiium, 

 Raster, lb. V, 2, 3. 



f They lire the Parucephukiphom Dioicu Asiphonohranchiaf.a of Blainviile. 



X This great genus constitutes the family Gunivstuina, Blaiav. 



§ Tioch. inennis, Chemn., V, clxxiii, 1/12 — 13 ; — Tr. Cookii, la., clxiv, lool ; — 

 TV. c<dutus, Id., clxii. 1536 — 37; — Tr. imbricafus, lb., 1532 — 33; — Tr. tuber, Id., 

 clxv, 1573 — 74; — Tr. sinensis, Ih., 1564 — 63; — Turbo pagodus, Id., clxiii, 1541 — 

 42; — Ti'.rho tectam-persicum, lb., 1543 — 44. 



