50 CLASS GASTEROPODA. 
the heart and gills under the belly, has given rise to many 
errors respecting the place of these animals. A simple in- 
spection of their nervous system led me to suppose, in my 
memoirs on the mollusca, that they were analogous to the gas- 
teropoda. A more exact anatomical investigation, made since 
then, and that given by M. Poli in his third volume, fully con- 
firm my opinion. The fact is, that there is but little difference 
between the heteropoda and the tectibranchiata ; notwith- 
standing which M. Laurillard believes their sexes to be sepa- 
rated. They have the faculty of distending their body, by 
filling it with water, in a way not well understood. Forskal 
comprized them all in his genus, 
PTEROTRACHEA, Forsk., 
But it has been found necessary to sub-divide them. 
CARINARIA, Lam. 
The nucleus, formed of the heart, liver, and organs of gene- 
ration, covered by a slender symmetrical shell, the point of 
which is bent backwards, and frequently raised by a crest, 
under the anterior edge of which float the feathers of the gills. 
On the head are two tentacula, and behind their base the eyes. 
There is one species in the Mediterranean, Carinaria cym- 
bium, Lam., Péron, Ann. du Mus. XV. iii. 15; Poli. ITI. xliv. ; 
Ann. des Sc. Nat. tome XVI. pl. i. 
Another, the Carinaria fragilis, Bory St. Vincent, (Voy. aux 
isles d’Afr. I. vi. 4.), is found in the Indian Ocean. 
Add Carinaria depressa, Rang. Ann. des Sc. Nat. Feb. 
1829, p. 136. 
The Argonauta vitrea of authors, Favanne vii. c. 2; Mar- 
tini, I. xiii. 163., must be the shell of a large carimaria, but 
the animal is not yet known. 
