LAS^A. 217 



Genus III. LAS^E'A*, Leach. PL V. f. 2. 



Body oval : mantle folded on the anterior side (being the 

 longer and larger end of the shell), so as to form a wide, but 

 incomplete, incurrent tube : the excurrent tube is very short and 

 inconspicuous, placed on the opposite side : foot long, tongue- 

 shaped, protruding when in motion through a slit in the ex- 

 current tube at its base. 



Shell roundish-oval : beaks straight : cartilage long and 

 cylindrical, divided or split lengthwise, and clasping the 

 hinge -plate, in each valve, on the smaller and narrower side 

 of the shell, being the posterior end : hinge containing in the 

 left valve a minute thorn-like cardinal tooth, and in each 

 valve two remarkably strong lateral teeth. 



The late Captain Brown proposed this genus in 1827, 

 on the authority of Dr. Leach, for the Cardiwn rubrum 

 of Montagu ; and although he says nothing about the 

 animal, and not much more about the shell, I think the 

 genus is a good one, and I therefore adopt the name 

 above given to it. M. Recluz, apparently unaware of 

 his having been anticipated, gave in 1843 another name 

 {Poronia) to the same genus; but his description is 

 positively incorrect. He says of the animal, that it has 

 on the posterior side two lobes, and two tubes which are 

 disunited ; and of the shell, that the hinge has two cardi- 

 nal teeth in each valve, besides lateral teeth, and that 

 the cartilage is placed in an oblique groove. It will be 

 seen that my description of the generic characters is 

 very different from that of M. Recluz ; and were it not 

 for the certainty that we both mean not only the same 

 genus, but also the same species, I could not believe 

 that our respective descriptions had been drawn from 

 the same object. The present genus is intermediate 

 between Montacuta and Kellia, and partakes of the 



* A meaningless name ; possibly a corrupt derivation from \cuaijiov, a 

 little shield. 



L 



