Lamarck's Genera of Shells. 257 



The situation of the heart and branchiae of the mollusca of this 

 order, is extremely singular; they are placed below the belly, and 

 in many of them are on the outside of it. In this respect, and in 

 the position of the animal whilst swimming, which is horizontal, 

 the heteropoda differ essentially from the pteropoda, which always 

 float in a perpendicular position. 



They seem to be more nearly allied to the cephalopoda, but differ 

 from them by having no arms on the head, no mantle, nor the two 

 horny, crooked mandibles, like a parrot's bill, which those animals are 

 furnished with : their organs of motion are also differently disposed. 



The body of these mollusca is gelatinous and transparent, and 

 the shell of some of them resembles that of the argonauta. 

 1. Carinaria*. 



Body elongated, gelatinous, transparent, terminated posteriorly 

 by a tail, and furnished with one or several unequal alse. Heart 

 and branchiee projecting beyond the belly, united in a pendant 

 mass, situated towards the tail, and enclosed in a shell. Head 

 distinct; two tentacula ; two eyes ; a contractile trunk. 



Shell univalve, conical, flattened at the sides, unilocular, very 

 thin, hyaline; summit convolute, spiral ; back of the shell some- 

 times furnished with an indented keel. Aperture oblong, entire. 



M. Bory de St. Vincent first observed this singular animal in his 

 voyage to the principal islands of the African seas, and gave a 

 figure of it, with its shell enclosing the principal organs. Subse- 

 quently MM. Peron and Le Sueur have given further details of 

 the animal, in the Annales du Musewn, vol. xv. p. 67. 



Type. Carinaria vitreaf. (Patella cristata. Linn.) 



Shell thin, hyaline, transversely sulcated ; back furnished with 

 an indented keel ; spire conoidal, attenuated ; apex very small, in- 

 volute; aperture contracted towards the keel. Southern Ocean. 

 PI. vi. Fig. 239. 



This shell, which M. Lamarck considers as the rarest, most 



curious, and most precious of all that are contained in the Museum 



of Natural History at Paris, was presented to it by M. de la Reveillere 



Lepaux, in the name of M. Kuon, who, after the death of Entre- 



* From carina, the keel of a vessel. f Glassy. 



Vol. XVI. S 



