﻿Lr.riDODESMA 237 



Genus LEPIDODESMA Simpson, 1896. 



Lepidodesma Simpson, Pr. U. S. Nat. Mus., 1896, p. 311. 



Shell large, thin, inflated, with a high, sharp posterior ridge 

 and a second fainter one above it, making the hinder part 

 widely biangulate ; beaks very high and full, their sculpture, 

 which extends over the whole shell, consisting of ridges that 

 follow the growth lines ; there are two rows of radiating 

 nodules, one on the middle of the disk, and a stronger one on 

 the post-ridge; ligament very large, wide, covered with con- 

 centric scales ; hinge line arched ; there are two pseudocardinals 

 in the left valve, the anterior elongated, running inwardly 

 across the hinge plate and ending abruptly ; a shorter, fainter 

 one stands behind it ; with two strong laterals, the inner the 

 higher, its edge reflexed upward, and suddenly truncate be- 

 hind ; there is one low, elongated pseudocardinal in the right 

 valve, and one lateral, which is reflexed upward; epidermis 

 folded into the hinge and scaly ; a single dorsal scar on the 

 inner side of each hinge plate ; muscle scars united, pallial line 

 distinct : beak cavities large and wide ; nacre very dull. Ani- 

 mal unknown. 



Type, Unio langiiilati Heude. 



I.EPrnoDKSMA i.ANGuiLATi (Heude). 



Shell large, scarcely subsolid, inflated, subtriangular, with 

 two distinct posterior ridges, which curve down in the middle, 

 the lower the higher, the two marking the limit of a wide, de- 

 cided posterior truncation ; base line nearly straight ; posterior 

 slope obliquely truncated ; ligament very large, dark brown 

 and covered with crescentic scales ; the pit in which it is 

 lodged extends forward under the beaks and is filled with epi- 

 dermal matter; beaks very high and full, their sculpture con- 

 sisting of coarse, doubly-looped and doubly-noduled ridges, 

 the bases of the loops and the nodules occurring on the pos- 

 terior ridges ; surface covered with very strong ridges, which 

 follow the growth lines ; epidermis greenish in young shells, 

 ash-colored in old ones ; left valve with two compressed pseudo- 



