246 GINGLYMACONCHA. 
ment, which has the power of throwing open the valves, even 
when the animal is removed from it: they are partially closed 
by the action of one or two adductor muscles, which rarely act 
without the aid of one or two adductor ligaments, which are 
sometimes, but very rarely wanting*. The lamella of which 
these shells are formed is secreted from the serous surface of 
the mantle, by which they are increased in their size during the 
growth of the animal. 
Their mouth is furnished with two lips, the angles of which 
are produced into lobes, which hang over one another. They 
have no eyes, tentacles nor maxillee (or jaws). 
The organs of respiration consist of four lamellee finely reti- 
culated, which are placed between the margins of the mantle ; 
the mantle is often attached to the anterior lower margin of 
the shell, an opening being left for the passage of water for 
respiration and nutrition ; the upper one for the exit of the ex- 
crement, as in the class Ascidia. 
Almost all the genera are furnished with a foot to enable 
them to move; in many genera they are immovably attached 
to their shells, and those who need not a foot either want it 
entirely or have it in a very slight degree of development. 
Several of the genera have a byssus, consisting of an unra- 
velled tendon, attached to the base of the foot, by which they 
adhere to other bodies. 
Mr. Wood, in the Introduction to his work on General Con- 
chology, asserts that those without syphons, and which have a 
foot, such as oysters, are of the lowest order of animated beings ; 
and yet he says that they are all mollusca, and that the dila- 
tations of the mantle which covers the back of the genus Cy- 
preea are wings. I would ask him from what work he has 
founded these ideas, which are totally incorrect ’—and again, in 
his Advertisement to the same work, “that, notwithstanding 
the attempts which have been made to form a more perfect 
arrangement, the structure raised by the great Swedish natu- 
ralist still remains unshaken?’’ I most willingly allow that it 
* Jn the year 1815 I made known to the Philomathic Society in Paris 
this discovery, which was published by Professor H. D. De Blainville in the 
Journal de Physique of the same year. 
