83 



MONOGRAPH OF THE GENUS 

 LIMA. 



Char. Gen. Molluscum acephalopodum unimusculosum. 

 Testa bivalvi, interdum libera, interdum bysso adhterente, 

 subeequivalvi, bi-auriculata, oblique ovali, radiatim costata vel 

 striata; margine ventrali antice producto, cardine recto, 

 edentulo ; foveola trigona, in medio areee centralis cartila- 

 ginem recipiente ; impressione musculari sublaterali : colore 

 albo ; epidermide fusco, tenui. 



The shells of this genus are generally equivalve, more or 

 less obliquely oval, with small triangular, lateral auricles. 

 The umbones are kept apart by a triangular disc in each 

 valve. In the centre of each is a pit containing the cartilage, 

 and the ligament is spread upon the surface at each side. 



In all the species, there is an hiatus at both sides of the shell, 

 although in several species it is very narrow. A byssus passing 

 through the anterior hiatus, occasionally attaches the shell to 

 sub-marine substances. 



Judging from the shells alone, the Limae would appear to 

 be closely allied to the genus Pecten, from which they differ 

 in having the umbones kept apart by the triangular disc, and in 

 the ventral margins being produced on the anterior instead of 

 the posterior side, so that the apex of the shell leans in the 

 opposite direction. All the shells are white, or nearly so, but 

 have a thin, transparent brown epidermis. 



DESCRIPTIONS. 



1. L. scabra (pi. xxi. f. 4, 5, 12.) Born. Mus. Cees. p. 

 110, Pecten aspera, Chemn. 7- p. 352. pi. 68. f. G52. Ostrea 

 glacialis, Gmel. p. p. 3302. Lam. &c. 



