42 M. Valenciennes on the Organization of Lucina and Corbis. 
However, whatever be the organization of the branchize of Mol- 
lusca, it is admitted and established by malacologists, that all 
the Acephala have four branchial leaflets. This general rule has 
hitherto been based on the study of several hundred animals of 
this class. 
Between the leaflets and near one of the extremities, called the 
anterior one, is the mouth, a round aperture terminating imme- 
diately in the esophagus, without any hard organ for the masti- 
cation, and without any external lingual tubercle; it is sur- 
rounded by small folds which bear the name of lips, and which 
are frequently ornamented with appendages or plaited filaments, 
varying somewhat according to the genera. Beyond the lips and 
on each side of the body there are two small triangular processes 
traversed by numerous ridges, which give to these organs an ap- 
pearance of branchial lamella); they are called the labial palpi. 
I have called attention to these external appearances of the 
Acephalous Mollusca to render more intelligible what Iam about 
to describe. I have now to communicate to the Academy an ob- 
servation opposed to the general rule of the four branchial lamin. 
The family of the Lucine is composed of mollusca which have 
only a single branchial leaflet on each side of the visceral mass 
and of the foot. This single branchia resembles that of the Ano- 
donta; it is large, thick, and formed of pectinated and anastomo- 
sing lamelle. I first noticed this smgular fact on Lucina jamai- 
censis. Surprised at. this peculiarity, which I found to be con- 
stant in all the individuals in the collection of the Muséum 
@ Histoire Naturelle, I was immediately induced to ascertain 
whether this difference occurred in other species of Lucina or in 
animals) allied to them. I observed the same conformation ina 
mollusk which had for a long time, been placed among the Ve- 
nuses, which Lamarek and his followers arranged im the genus 
Cytherea, but which I have been led to place near to Lucina from 
the insertion and nature of the ligament of the two valves; I 
mean the Venus tigerina of Linneus. My previsions have there- 
fore been verified in this respect, for the far more important cha- 
racter of the unity of the branchial leaflet leaves not the least. 
doubt respecting the affinity of the two mollusca, which moreover 
resemble each other in several other details of their organization, 
although the shells differ widely with the exception of the liga. 
ment. 
A third species well-known to conchologists, Lucina colum- 
bella, Lam., from the seas of Senegal, has likewise but one single 
branchial leaflet on each side of the foot. And lastly, a small 
species very abundant on all the sandy coasts of the Mediterra- 
nean, Lucina lactea, Lam., which Poli formed into a new genus 
under the name of Loripes, has also only one branchial lamina. 
But this is not all. In the Polynesian Archipelagos an ace- 
