JIOLLUSCA. 
50 
their foot, whicli, instead of forming a horizontal disk, is compressed 
into a vertical muscular lamina, which they use as a fin, and on the 
edge of Avhich, in several species, is a dilatation forming a hollow 
cone, that represents the disk of the other orders. Their hranchise, 
composed of plumiform lobes, are situated on the hind pai-t of the 
back, directed forwards, and immediately in their rear are the heart 
and a small liver, Avith part of the viscera and the internal organs of 
generation. Their body, a gelatinous and transparent substance 
lined Avith a muscular layer, is elongated and usually terminated by a 
compressed tail. There is a muscular mass belonging to the mouth, 
and a tongue furnished Avith little hooks ; the oesophagus is very long; 
their stomach thin ; tAVO prominent tubes on the right side of the 
visceral bundle afford a passage to the feces, semen or ova. They 
-nsiially sAvim on their back Avith the foot upAvards*'. They have the 
faculty of distending their body by filling it Avith Avater, in a Avay not 
Avell understood. Forskahl comprised them all in his genus. 
Ptkrotrachea, F orsk. 
But Ave have been compelled to subdivide tliem. 
CarinariAj Lam.f 
Have the nucleus formed of the heart, liver, and organs of generation, 
covered by a slender, symmetrical and conical shell, the point of 
Avhich is bent backAvards and frequently relieved by a crest, under 
AA’hose anterior edge float the feathers of the branchiae ; tAvo tenta- 
cula on the head, and the eyes behind their base. 
One species, Carinaria cymbium, Lam.; Peron, Ann. du 
Mus., XV, iii, 15 ; Poli, III, xliv ; Ann. des Sc. Nat., tome XVI, 
pi. 1 , inhabits the Mediterranean. 
Another, the Carinaria fragilis, Bory Saint- Vincent, Voy, 
aux Isles d’Afr., I, vi, 4 :};, is found in the Indian Ocean. 
* Tliis mode of natation induced Peron to think that the natatory lamina was on 
the hack, and the heart and branchiae under the belly, and has given rise to many 
errors as respects the place of these animals. A simple inspection of their ner- 
vous system led me to suppose, in my Memoirs on the Mollusca, that they 
%-ere analogous to the Gasteropoda. A more exact anatomical investigation, made 
sine; then, with that given by M. Poli in his vol. Ill, fully confirms my supposition. 
Tlie fact is, that there is but little difference between the Heteropoda and the 
Tectihranclduta, notwithstanding Avhich, M. Laurillard belieA’es their sexes to be 
separated. 
p Forskahl comurised all these animals in his genus Pterotrachea, for which 
name Brugi^re substituted that of Fihola. Plrron having divded tlie genus, 
appropriated the name of Cannaria to those with a shell, and that of Firota to the 
others. Rondelet gives the Cunnerm, but without its shell. — “ De Insect. Zooph. 
cap. XX.” 
+ Add, Carinaria depressa, Rang. Ann. des Sc. Nat., Feb. 1829, p. 136. 
