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Show 328 MOLl .. USCA. of combs, and are concealed in a dorsal cavity, widely open above the head. N ear1y all of them have ~ turbin~ted s~ell, a mouth some-times entire, sometimes furmshed With a siphon, and roost generally susceptible of being more or less perfectly closed by an operculum attached to the foot of the animal behind( I). The ''fuBULIBRANCIIIA T A Have a shell resembling a more or less irregularly pointed tube which attaches itself to various bodies. Their branchirn consist of a single range along the left side of the roof of the branchial cavity. The ScuTIBRANCHIATA Have branchire similar to those of the Pectinibranchiata; but the sexes are united, so that fecundation takes place without a mutual copulation, as in the Acephala. Their shell is very open, and in several forms a non-turbinated shield; the oper· culum is always wanting. The CYCLOBRANCHIATA, Hermaphrodites like the Scutibranchiata, hav~ a shell co~· posed of one or several pieces, but never turbmated nor Wt~h an operculum ; their branchire are attached under the margm of their mantle, as in the Inferobranchiata. ORDER I. PULMONEA(2). The Pulmonea are distinguished from the other Mollusca . d . uch a man· (1) N.H. Sometimes, as in Vcrmctus, &c., the foot IS recurve m 8 ner that the operculum is before. (2) M. de Blainville prefers the term PuLMONOBRANCHIATA. GASTEROPODA I>ULMONEA. 329 by respiring elastic air through a hole opening under the margin of the mantle, and which they dilate and contract at will; they have. no branchi::e, but a mere net-work of pulmonary vessels whiCh creep over the parietes of the respirator cavity and chiefly on its ceiling. y Some of the.~ are terrestrial; others are aquatic, but are compelled to. VISit the ~urface from time to time for the purpose of opemng the orifice of their pectoral cavity, or torespire. They are all hermaphrodite. The PULMONEA TERRESTRIA Have generaHy four tentacula; in two or three only of a very small size, the lower pair are not to be seen. ' Those which possess no apparent shell, form in the Linncean system the genus LIMAx, Lin. Which we divide as follows: LrMAX, Lam. The body elongated, aud the mantle, a dense fleshy disk which is con~ned. to the forepart of the back, merely covering the pulmonary cavity; m several species it contains a small, flat and oblong shell, or. at l~ast a calcareous concretion in place of it. The respiratory orifice IS on the right of this species of shield, and the anus on the margin of that orifice. The four tentacula are protruded and retracted, e_:olving themselves like the inverted fingers of a glove, and the head Itself can be partly withdrawn under the disk of the mantle Th e gem· tal organs open under the upper right tentaculum. The. mouth has only an upper jaw, resembling a dentated ct·escent which enables these animals to gnaw fruits and herbs, which they ~o with 50 much voracity as to effect considerable injury. The stomach is elongated, simple and membranous. M. de Fhussac distinguishes ARioN, Fer., ~here the respiratory orifice is towards the anterior part of the shteld ' w. hicl1 mere1 y conta·m s a .~e w calcareous granules. Such is L~max 1'Ujus, L.; Ferussac, Moll. Terr. et Fluv., pl. i and iii. It is everywhere to be met with in wet weather and is some- V OL. II.-2 R ' \ |