LEPTON. 77 



branchial siphon ; but there are mantellar folds, which, with 

 the great ventral opening, amply provide for the admission of 

 the water. 



The animals of this interesting group exhibit, in the tenta- 

 cular filaments and curious foot, as well as in the sculpture of 

 their shells, very considerable variation from KeUia rubra and 

 Kellia suborbicularis, the types of one of the genera of the 

 family in which they have been located by authors, doubtless 

 from the want of knowledge of the animal. Taking into 

 consideration that the Leptons have many of the attributes 

 of the Arcades, and especially giA'ing due weight to the re- 

 markable similarity between the foot of Lepton squamosum 

 and the Pectunculus pilosus, I am almost induced to believe 

 that it is in a false position, in connexion with the Kelliadce, 

 and that it ought to follow or precede Galeomma, which, with 

 me, is an undoubted genus of the Arcadce. 



The punctures of this species and of L. convexum are in the 

 test ; with respect to its congener, the L. nitidum, it has 

 been stated that it is smooth and without punctures : this is 

 a mistake, as I can show fifty specimens not only well- 

 marked on the greenish epidermis, but in the substance of 

 the shell. 



I have the satisfaction to state, that I have observed another 

 live L. squamosum, and also obtained full notes of the animal 

 of one of our great desiderata, the L. nitidum, from a most 

 lively animal, which for several days gave me every facility 

 for examination. The L. squamosum, just alluded to, was 

 kept thirty-four days in a glass of sea- water, changed daily, 

 and was apparently as vigorous as when first placed in captivity ; 

 it thus appears that the Conchifera can exist for a long time 

 in pure sea- water, on the animalcules it contains, though that 

 aliment may not be their sole resource in freedom. 



I may observe, that the habitude of crawling and swimming 

 with the foot uppermost in Lepton, and in several other minute 

 bivalves, perhaps in all, shows the close alliance of the Acephala 

 with the Gasteropoda, all of which, in their minute condition, 

 have precisely the same peculiar system of dorsal natation. I 

 ought to have mentioned that the liver is light green and 



