218 KELLIID.E. 



leading characteristics of each. With the former it 

 agrees in having the cartilage placed at the shorter end 

 of the shell, a position contrary to that in Kellia, and 

 with the latter in the mantle being folded on the ante- 

 rior side, though not so completely as in that genus. 

 The position of the cartilage or ligament is by no means 

 unimportant, because it indicates the posterior side ; and 

 the empty shell thus serves to determine the place, and 

 often the nature, of the organs which had composed the 

 frame of its late occupant. 



It is very probable that the shell which Adanson 

 called " Le Poron " belongs to this genus ; but his 

 notice of it is unusually brief and obscure. He says that 

 it has two small triangular teeth in each valve, which 

 form the hinge, that it is at most only two lines in dia- 

 meter, and that it is whitish and sometimes of a violet 

 colour, chiefly towards the hinge. He evidently did not 

 know the animal, for he included the Poron among the 

 species of his genus Chama, which he described as having 

 three openings in the mantle, two of which take the form 

 of a rather long tube. It would be a waste of etymolo- 

 gical research were we to endeavour to trace the derivation 

 of the word " Poron." Adanson tells us, in the preface 

 to his most admirable work on the Mollusca of Senegal, 

 that he preferred inventing such chance names as had 

 the least meaning, and had no relation to other names 

 or known objects. Perhaps Dr. Leach had the same 

 idea in selecting some of his generic names. However 

 that may be, in his posthumous work on the Mollusca 

 of Great Britain he seems to have changed Lascea for 

 the more classically correct name of Autonoe, placing it 

 in the family Venerida, although calling the species (after 

 describing it) " Lasea rubra." 



The Lascecs are of a minute size, and usually inhabit 



