42 M. Valenciennes on the Oi-ganization of Lucina and Corbis. 



However, whatever be the organization of the branchiae 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 oesophagus, 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 lamellae ; they are called the labial palpi. 



I have called attention to these external appearances of the 

 Acephalous MoUusca to render more intelligible what I am about 

 to describe. I have now to communicate to the Academy an ob- 

 servation opposed to the general rule of the four branchial laminae. 

 The family of the Lacing is composed of moUusca 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 lamellae. I first noticed this singular 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 Museum 

 d^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 in a 

 moUusk which had for a long time been placed among the Ve- 

 nuses, which Lamarck and his followers arranged in 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 Linnaeus. 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 afiinity of the two moUusca, which moreover 

 resemble each other in several other details of their organization, 

 although the shells difi'er widely with the exception of the liga- 

 ment. 



A third species well-known to conchologists, Lucina colum- 

 hellttf 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- 



