350 



aiOLLUSCA. 



The Aquatic Pulmonea have only two tonirioiila. They come ever and anon to the 



surface to breathe, so that they can only inhal^it wiiter:^ of ineoiisidcrahlc deptli : thus they 

 hve in frryh waters or in brackish pools, or at Uast iirar the sides and mouths of rivers. 

 There aru some amongst them without a shull : such is the 



Onchidium, Ciiv."^ 



A harge fieshy ch:iak, of llic shape of a buckler, ovcrlaji^s the foot on every sirlc, and even covers the 

 head when tliis is contracted. It has two h:)iig retractile teiitacida, and over tlic month a vcib sinu- 

 atcd, or formed of two triangnlar compressed lobes. The aims and air-passage are nndcr the hinrler 

 margin of the cloak, where, a little deeper, we find al.^o the pulmonary sac. Kear tliem, to the right, 

 is the opening of the female organs, while, on the cuiitiary. tliat of the male organ is under the right 

 tentaculum ; and these two orifices are united by a groove wliich runs under and along the right edge 

 of the cloak. Destitute of jaws, they have a rauseidar gizzard, succeeded by two membranous stomachs. 

 Several species inhabit the coasts of the sea, but always in such a situation that tliey are uncovered at 

 ebb tide, when tliey ot)taiu the air necessary to respiration. 



The Aquatic Pulmonea, with perfect shells, have been placed l)y Linnaeus in his genera Helix, Bulla, 

 and Volufoy whence they ought to be withdrawn. In Helix were the two follo\^ing genera, whose aper- 

 ture, as in Helix, had its inner [or pillar] margin protuberant and arcnate : — 



TtiE Plaxorbis, Brug., — 

 Had already been distinguished from Helix l>y Bruguieres, and even previously by Guettaid, hecanse 

 the whorls of their shell, rolled up nearly on a level, enlarge insensibly, and the mouth is wider than 

 deep.f It contains a Snail with long, slender, filiform teutacnla, at the inner base of which the eyes 

 are sitiiatrd. It can exude, from the margin of its cloak, a copious red liijuor, which is not to be mis- 

 taken for ii^ blood, The stomach is nmbcular, and the food vegetable, as in the Limncea;, which are 

 the faithful companions of the Planorbcs in all our btagnaut waters. 



The LiMNiiEUs, Lam., 

 Were separated from the Bulirnns of Bruguicres, because, notwithstanding the siniilarily of the shells, 

 the mari^in of the Lhnnecs is sharp-cdgcil anrl not reflected, anrl their colnniella has an obhque fold. 



lell is thin : the animal has two compressed, 

 triangular tentaenla, with the eves sessile at 

 inner hase. They iVcd upon jilaiUs and seeds; 

 leir st(nnacli is a very rmiscnlar gizzard, fur- 

 willi a eiop. Ilennaiihrodites, after the fa- 

 shion of their order, they have the female organ rather 

 widely apart from the other, — a stmclnre which 

 compels them to copniate in snch a maiuier that the 

 individual acting as a male to his mate is the fe- 

 male to a third, and from this peeuliarify we occa- 

 i-ii;. 11.2— ].imii.-cn siaKniaiis. sioually find tlicni joined together in long strings. 



Thcv ahonnd in stagnant waters : and they are found plentifully, as well as the Planorhes, in marly 

 or calcareous bcils, which we thus discover to liave been deposited from fresh water. 



TuR Phys-e,— 



Vhich were arranged arbitrarily among the Bnike, have the shell of Linuia"'us, but still thinner, and 

 there is no fold on the columeUa. The animal, wdien it swims or crcei)S, covers its shell with the two 

 pectinated lobes of the cloak : it has two long setaceous teutacnla, which are bulged at the base \\here 

 the eyes are placed. 



Tlie speeies are .small, ami live in clear pninls. One of theni yBulh' /on/i/ni/is. Lam.), hos its \vhorls sinistral, 

 [and tliis, indi.'ed, i.s the unly certain chacieter wlneli 'h-stiii^odsbes the ,L;-enus tVnni Lirnnaais.]-|- 



* ftl.Jij DUiinillij liPiM ul.anyLil Uiu iiJimc Ouutjiiliuui i.il'j Prnniui, 

 anrl trajisfers tliu first to the Vagiiiulus. He places Pcruiiia 

 aiiiofiK'st his CycUibranchia; but I cannot perceive miy tciil (HfTcreiiec 

 between ihpir rcspimtory nru.in ami ihiit of the other Pulmonea. [As 

 this jjeiius ia not tlie Onchjdium of Buchanan, as CuvUt supposed, 

 M. 'le Ferusadc proposes to nume it Onchia.] 



t Snw.Tl))- m 



iT sivUlT'il.— V. 



t When the 



: cl.vik siUlkitnUy -Lniple 

 IS is the .-Iwphiprplta of 



!i(i the eloal^ eiiiire, the 



