44 M. Valenciennes on the Organization of Jiucina and Corbis. 



only mentioned Loripes in order to verify the observations of the 

 Neapolitan anatomist respecting the foot of this moUusk, it may 

 be conceived why he has not pointed out the absence of one pair 

 of branchise. I must however add, that the Lucina lactea, ex- 

 amined by these expert zoologists, is a very minute mollusk of 

 one to two centimetres in diameter, while I have been able to 

 examine hucina from five to six centimetres in diameter ; the 

 observation was therefore easy to make ; and when once 1 had as- 

 certained the possibility of the existence of one single branchial 

 lamina in Lmcina jamaicensis and L. tigerinay I could readily de- 

 tect the same organization in the smallest individuals of Lucina 

 lactea from the Mediterranean. 



The conformation of the foot of these mollusks, which had at- 

 tracted the attention of Poli, is very remarkable ; but this anato- 

 mist has not given a very complete description of it, which it 

 nevertheless deserves. This foot is a fleshy cylinder folded back 

 on itself so as to be hidden between the plates of the mantle of 

 the mollusk, for it is frequently twice as long as the diameter of 

 the animal. When not contracted it is much longer. It is re- 

 markable that it is hollow throughout its entire length, and that 

 this tube opens directly and widely into the spaces of the visceral 

 cavity. I have verified this fact by following the canal in its en- 

 tire length either by cutting it open or by injection, when the 

 spaces of the visceral mass became filled, and I also thought I 

 could perceive traces of injected vessels. This result will not 

 appear surprising if we call to mind the observations which 

 M. Milne Edwards and I have communicated to the Academy on 

 the circulation in Mollusca, and on the large communications ex- 

 isting between the visceral cavity and the sanguiniferous vessels 

 of the Acephala. But there is a new fact here deserving of 

 especial attention, from its importance for the physiology of Mol- 

 lusca; it is, that the inner cavities containing the blood are 

 placed by means of the canal of the foot in Lucina in free com- 

 munication with the surrounding element. The heart and the 

 other viscera which I was able to observe of these animals, pre- 

 served in spirit, did not appear to offer anything remarkable. 



[It is to be regretted that M. Valenciennes has not accompanied 

 his notice of the single gill on each side of the Lucina with some 

 account of its structure : from the statement that it is large, thick, 

 and formed of pectinated and anastomosing lamella, it may agree essen- 

 tially with the apparently single gill in the genera Pholadomya and 

 Anatina, described by Prof. Owen in his ' Lectures on the Inver- 

 tebrata,' 1843, p. 283, where the exception to the ordinary struc- 

 ture and number of the gills in the Lamellibranchiate Acephala is 

 distinctly pointed out as follows : — 



'* The two branchial lamellae of one side are usually connected with 

 those of the opposite side by their posterior extremities only ; but 



