52 
MOLLUSC A. 
We are not so certain tliat Ave sliould place there the 
Phylliroe, Pero7J., 
An du Mas., XV, pi. ii, f. 1, where the transparent and strongly com- 
pressed body has a snout before, surmounted by two long tentacula 
without eyes, a truncated tail behind, and Avhich allows the heart, 
neiwous system, genital organs of both sexes to be seen through the 
integuments. The g'enital orifices and that of the amxs are on the 
right side, and sometimes a tolerably long penis is visible ; I can find 
no other organ of respiration than its thin and Avascular skin*. 
ORDER VI. 
PECTlNIBRANCHIATAf. 
This order forms, beyond all comparison, the most numerous divi 
sion, inasmuch as it comprises the Avhole of the spiral univahms, and 
seA^eral that are simply conical. Their branchiae, composed of nu- 
lAierous lamellae or strips laid })arallcl Avith each other, like the teeth 
of a comb, are attached on one, tAvo, or three lines, according to the 
genus, to the ceiling of the pulmonary cavity, Avhich occupies the 
last Avhorl of a shell, and Avhich has a large opening betAveen the 
edge of the mantle and the body. 
In tAA’o genera only, Cijclostoma and Helicina, do Ave find, instead 
of branchia?, a A^ascidar netAvork, covering the ceiling of a cavity, in 
other respects very similar ; they are the only ones that respire the 
natural air ; all the others respire Avater. 
All the Pectinibranchiata have tAvo tentacida and tAVo eyes, some- 
times placed on particular pedicles, and a mouth resembling a more 
or less elongated proboscis; the sexes are separated. The penis of 
the male, attached to the right side of the neck, cannot usually be re- 
tracted Avithin the body, but is reflected into the cavity of the branchixe; 
it is sometimes very stout, and the Paludina is the only one Avhich 
can retract it through an orifice perforated in its right tcntaculum. 
The rectum and oviduct of the female also creep along the right side 
of the cavity, betAveen them and the branchiae is a lacculiar organ 
composed of cells, from Avhich' exudes an extremely viscid fluid ; 
this forms a common envelope Avhich contains the OA^a, and Avhich is 
*■ These observations are made from individuals presented to me ly M. Quoy. 
M. de Blainville makes a family of Phiiliroe, Avhich he names PdUosoma, and which 
is the third of his Aporobranchiala ; the others are Hyalic, &c. 
-f- M. de ClainA'ille’s sub-class Paracepkedophora Pioica. 
