LAMELLIBRANCHIATA. 161 



Leiopteria Rafinesquii. 



PLATE XV, FIG. 11 ; PLATE XX, FIGS II, 7 ; and PLATE LXXXVIII, FIGS. 27, 28. 



Leiopteria liafiiies lull. H.\i,L. Pal. N. Y., vol. v, pt. 1. Plates and Exiilanations : PI. 15, tig. 11; pi. 20, 



tifjs. G, 7. Jan., 1S83. 



Shell of medium size, sul)-rhomboidal ; body rather narrow above, obliquely 

 ovate ; height equalling or greater than the length ; margins regularly 

 curved ; the post-basal side extended ; anterior side sometimes nearly 

 straight for a short distance below the ear. 



Left valve convex, gibbous on the umbo. Right valve less gibljous. The 

 right valve supposed to belong to this species is convex on the umbo, and of 

 moderate convexity below ; the height is considerably greater than the 

 length, and the body of the valve less distinctly defined than in the left 

 valve. 



Hinge-line straight; from the anterior side of the l)eak to the posterior 

 extremity it is about equal to the length of the shell. 



Beak of the left valve acute, directed forward, very prominent, situated 

 at the anterior extremity of the shell. Umbonal region gil^bous, subtending 

 an acute angle. 



Ear short, convex, obtuse, with a brotid undefined vertical sulcus and shal- 

 low byssal sinus. Wing moderately large, flat ; margin concave ; extremity 

 acute. 



Test thin, marked by regular, concentric lines of growth, which are more 

 crowded upon the cardinal expansions. The strise aij,e raised at intervals 

 into strong, elevated lamellae, which are conspicuous on the cast, and more 

 crowded and prominent on the anterior side. The right valve referred to 

 this species is marked by concentric wrinkles, which are well-preserved on 

 the anterior side, with distant, elevated, lamellose strise on the wing and the 

 margin of the hinge. 



Internal characters unknown. The ligamental area appears to be marked 

 by a groove along the wing parallel to the hinge-line. 



Three characteristic specimens have respectively the following dimen- 

 21 



