356 



MOLLUSCA. 



tentaciila, longitudinallv cleft as in Ploiirobranclins, and at their inner liases are the ryes : between 

 tliem is a kind of prolKiscis, perhaps an organ of t^oneration. There is a large coneyvi.^ space in the 

 anterior margin of tlie foot, the edges of -whicli ran he drawn together like the month of a pnrs-e ; and 

 at its bottom is a tubercle pierced with an orifice, which is perhaps the mouth, and is surmounted by 

 a fringed membrane. The inferior surface of tlie foot is smooth, and serves the animal to crawl on, as 

 in other Gasteropodes. It carries with it a hard, flat, irregularly-rounded shell, thickest in the centre, 

 with sharp margins, and lightly marked with concentric stria?. It was supposed at lirst that the shell 

 was attached to the foot, but more recent ohscrvations have proved that it is upon tlie cloak, and in its 

 usual place. 

 [T\vo spL-cics liave been discovered : one in the Indian Ocean, the other in tlie ^duditerranean.] 



THE FIFTH ORDER OF THE GASTEROPODES. 



THE HETERurODA, Lam.* 



The Ili'tcropocla arc ilistinguislied from all otlier MoUusca by their foot, wliieh, instead of 

 fonmny a horizontal disk, is coniiircsscd into a vertical muscular lamina, which they use as a 

 tin ; and on the edge of Avhicb, in several species, is a sucker in the form of a hollow cone, that 

 re|ircscnts the disk of the other orders. Their branchia:-, formed of plumose lobes, are situ- 

 ated on the hinder part of the back, and point forwards; and immediately behind them are 

 tlie heart and liver, of inconsideralde size, with a portion of the viscera and the interior organs 

 of generation. The liody, of a transparent gelatinous substance, sheathed with a muscular 

 lajer, is eIong:ate, and generally terminated with a compressed tad ; the mouth has a muscular 

 mass and a tongue garnished with little hooks ; the gullet is very long; the stomach thin; 

 two prominent tubes, on the right side of the bundle of the viscera, serve as passages to the 

 excrements, and to the eggs or somen. They swim, in ordinary, in a reversed position; and 

 they can inflate the liody with water in a manner which is not yet well understood. 



Forskal comprised tliein all under hi^ genus P/rru/rachPO, \\hieh it is necessary to siilnlivide. 



The C.\rinari,\, Lam., — 

 Has tlie nucleus (forrued Ijy the heart, the liver, and organs uf generation,) covered with a tliiu, sym- 

 metrical, conoid shell, with the point curved 



backwards, and often raised into a crest; under 

 its aiito'iur mai'i^in, the plumes of the branebiic 

 tloat ; on the head are two tcntacula, and the 

 eyes are behind their roots. f 



(")iie species {Car. ri/mhium, Lnni.) inhabits tlie 

 Mediterranean; another the Indian Ocean {Car. 

 fran'dis, B. St. Vincent). 1\\q Anjoiiauia rilrea of 

 autliors may be a Cariuaria, bat it.s animal is un- 

 known. 



The Atl.vnta, Le^^nenr, — 

 FrcHU the obsiTvatiniis of M. Kang, should be 

 auinuils of this order, whose shell, in })lace nf 

 being expamled, has a narrow cavity, and a 

 spire rolled up on the same plane: it.s con- 

 tour is raised into a thin crest. They are very 



small shells of the Indian Sea ; and in one of them, Lania\K)n believed that he had found the original 



of [he Ammonites. 



' M. (IL IJli.-.rivillc innKes a f.-imily of tlji.s orJur, n-hicli 

 Nrrtnpodii, iirid uiiilcs ihcni in his Niiclrobriindiiiilti with anotlier 

 fiiniily iiRMiei] tlic Pteriipoda, coiiti)risin({, liowevcr, only Lii 

 my Pttropudi.s. He adds to it, upon 1 know uot what coiija^'ture, lln: 



