GASTEROPODA PECTINIBRANCHIATA. 53 
deposited with tliem. The figure of this 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 enaljle the animal to 
lireathe without leaving its shelter. There is also this distinction 
between the genera — some of them have no operculum ; the species 
differ from each other by the filaments, fringes, and other ornaments 
of the head, foot, or mantle. 
These Mollusca 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. 
7' R O C H O I D A , 
This fcimily is known by the shell, the aperture of which is entire, 
Avithout 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. 
Titocms, 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 that have no umbilicus, there are some in Avhich the colu- 
mella, that has the form of a concave arch, is continuous with the 
external margin, Avithout any projection. It is the angle and ])rojec- 
tion of this margin Avhich distinguishes them from Turbo — Tecta- 
riiwi, Montf. § 
* For Aturex, see Lister, 881, Easter, Op. Subs., I, vi, 1, 2; for Burduu/ii, 
Easter, Ib. Y, 2, 3. 
-j- Tliey are the Parucephulojihoru Ltiuiru Asiphonabrancldata of Elaiiiville. 
J This great genus constitutes the family Gouiostuma, Elainv . 
§ Ti'och. inermis, Chemn,, Y, clx.xiii, 1712—13; — Tr. Ciiukii, Id., cl.\iv, 1551; — 
Tr. ciilutus, III., cLxii. 1536 — 37; — Tr. imbricalus, Ib., 1532 — 33; — Tr. tuber, Id., 
clxv, 1573 — 74; — 'Tr. sinensis, Ih., 1564 — 65 ; — Turbo pagodus, Id., elxiii, 1541 — 
42 ; — Turbo tectuni-perskum, Ib., 154.3 — 14. 
