﻿1 62 I.AMI'SII.IS 



Group of LampsUJs alata. 



Shell obovatc, strongly wins:e(l, siibsolid. with a slight pos- 

 terior and snperpostcrior ridge ; epidermis thick, dark, show- 

 ing irregular growth lines; hinge teeth generally well devel- 

 oped ; nacre dark jnirple : female shell greatly developed in 

 post-basal region. Animal having the ovisacs very numerous 

 and ( "inc ; niarsni)ium large; inner gills united to abdominal sac 

 throughout. 



Lampsius ai.ata (Say). 



Shell large, inequilateral, somewhat obovate, rather com- 

 pressed, subsolid. narrowed in front where it is rounded in 

 adult shells, but in the young shell it has a small angular dor- 

 sal wing; beaks low, compressed, their sculpture very faint, 

 consisting of feeble, broken ridges or sometimes of nodules, 

 which show a slight tendency in the direction of double loop- 

 ing; there is a low but rather pinched up ridge running from 

 the beaks down the posterior slope of the shell to its edge, and 

 above this it is carried up into a high triangular dorsal wing, 

 which is beautifully developed in young shells, but usually is 

 broken away in old ones ; below the upper posterior ridge 

 there is often a second ridge, which reaches to the extreme 

 posterior part of the shell ; posterior end of the shell wide 

 and rounded : surface with irregular, concentric sculpture, 

 brownish, blackish or olive-green, sometimes faintlv raved 

 in young specimens ; in adult shells the unbonal region is 

 reddish-brown. Left valve with ragged, generally compressed 

 pseudocardinals, with sometimes a vestige of a third above 

 the anterior one, and two remote, curved laterals ; right valve 

 with two pseudocardinals. the lower the larger and one high, 

 truncated lateral ; muscle scars large, the anterior appressed. 

 posterior scars faint ; beak cavities shallow ; dorsal scars 

 numerous, in a row running downward ; ligament and es- 

 cutcheon large; nacre coppery-purple, somewhat thickened 

 in front. The female shell has a large, rounded marsupial 

 swelling at the extreme post-basal part and is generally sub- 



