﻿LAMPS! LIS l8l 



Group of I,ampsi!is gracilis. 



Shell large, thin, elliptical or slightly obovate, with a high 

 posterior and an anterior wing, not greatly inflated ; beaks 

 low; epidermis rather smooth, often feebly rayed, dull colored, 

 but usually glossy : hinge line slightly and rather regularly 

 curved ; teeth compressed, pseudocardinals but feebly and often 

 imperfectly developed ; nacre purplish-tinted, dull. Shell of the 

 male and female nearly alike, the latter scarcely swollen at post- 

 basal region. Animal having the mantle greatly thickened at 

 the posterior end. and double and thickened at the post-base, 

 where it is often crenulate or toothed on its inner border, and 

 has the outer developed into a flap; inner gills united to the 

 abdominal sac throughout ; marsupium enormous, composed of 

 a great number of delicate, semiradiating ovisacs, projecting 

 far below the inner gills in a semicircle. 



Lampsilis gracilis (Barnes). 



Shell large, thin, obovate. subcompressed to subinflated, with 

 generally low compressed beaks having very feeble sculpture, 

 which shows a tendency to be doubly looped ; posterior ridge 

 almost wanting, there being two or sometimes three radial 

 raised lines on the posterior slope ; there is a moderately de- 

 veloped posterior wing, which is broken away in adult speci- 

 mens showing the long ligament, and in front of the hinge the 

 young shell is angular; surface rather smooth, with faint, ir- 

 regular growth lines, greenish-yellow or pale smoky-brownish, 

 sometimes feebly rayed, often rayless, the posterior slope dark 

 green and generally rayed ; left valve with two feeble, com- 

 pressed pseudocardinals and two remote, often imperfect, lat- 

 erals ; right valve with one pseudocardinal and one truncate 

 lateral ; beak cavities shallow, showing a row of ill-developed 

 muscle scars running in the direction of the retractor muscle 

 scar ; adductor scars large, faint, the anterior irregular ; nacre 

 faint purplish and bluish. Generally the male and female are 

 much alike, the former is sometimes a little rhomboid and 

 again it ends in a wide, rounded point about on the median 



