GASTEROPODA PJJCT1N1BRANCHIATA 



< '\TLO.STO\M. l.'im* 



The Cyclostom;r should he distinguished from all the others be- 

 cause they an- terrestrial, as instead of branchiae, the animal has 

 merely a vascular network spread over the parietcs of its pectoral 

 cavity. In every other resect, however, it resembles the other 

 iiniiuals of this family: the respiratory aperture is formed in the 

 s;nur way above the head by a great solution of continuity; the 



- an- separated : tin- penis of the male is large, fleshy, and re- 

 llected into the pectoral cavity ; the two tentacula are terminated by 

 blunt tubercles, and two other tubercles, placed on their external 

 base, support the eyes. 



'I'll-- shell is a spiral oval, with complete whorls, transversely and 

 finely striated, and its aperture, in the adult, is surrounded with a 

 sin ill ridge. It is closed by a small round operculum. Found in 

 woods, under moss, stones, &c. 



The most common is the Turbo eleyans, List., 27, 25, about 



six lines in length and of a greyish colour; found under all the 



mos- 



VALVATA. Mull. 



The Valvatae inhabit fresh water; their shell is convoluted in 

 almost one plane like that of a Planorbis, but the aperture is round, 

 and furnished with an operculum ; the animal, which has two slen- 

 der tentacnla. with the eyes at their anterior base, respires by means 

 of branchi;e. In a species found in France, 



r///r. cristata, Mull.; Drap., I. 32,33; Gruct-Huysen, Nov. 

 Act. Nat. Cur. X, pi. xxxviii, the branchiae, formed like a 

 feather, project from under the mantle and float externally, vi- 

 brating with the breathing of the animal. On the right side of 

 the body is a filament which resembles a third tentaculum. The 

 foot is divided, anteriorly, into two hooked lobes. The penis 

 of the male is slender, and reflected into the branchial cavity. 

 The shell, which is hardly three lines broad, is greyish, flat, 

 and umhilicated. Found in stagnant watcrj. 



It is here that we must place the completely aquatic shells, or 

 those respiring by branchi;e, which belonged to the old genus HELIX; 

 i.e.. those in which the penultimate whorl forms, as in the Helices, 

 Lymn;v;i\ See., a depress. -u which gives tin- aperture more or less of 

 the figure of a crescent . 



The three fnxt gmera are still closely allied to Turbo. 



* Tin- r//. /,,/,,irf and thr llrliri,n-s form the order of the PULMONKA OPKRCI-- 



I.ATA f'f Iff, cl I-Yni-mio. 



f Add. Tarlm Unri.Hi. I.M., -26, '24 : T. lalxo, List., 25, 23; T. dubitis, Bora., 



Mil. :,, 6; T. /iifoi/iv. Clu-iun., l\. <-\xiii. 107:,. 



WV >hi)ulil (listiniruMi, amonir thr fo--i!s the Cyclostoina mumia of Lain., Biongn., 

 Ann. iln Mil-.. \ \ . \\ii, 1. 



* Add. r,ilruta plawrhis, Drap.. I. .u. :i'. ; I'. ;/,,.(/(!, Id., 3638. 

 Thr> ntn-titiitc tin- 1 i bIFttOrrOM \ Ulainville. 



