LAMELLIBRANCHIATA. 91 



PTERINEA, GoLDFUss. 

 Pterinea grandis, n. sp. 



PLATE LXXXm, FIG. U. 



Shell very large, capacious, oblique, sub-rhomboidal, body broadly ovate ; 

 length about one-fifth greater than the height ; margins regularly rounded, 

 broad along the base, and a little produced on the posterior side. 



Left valve convex. Right valve unknown. 



Hinge-line straight, apparently somewhat less than the length of the 

 valve, [imperfect in the specimen.] 



Beak obtuse, prominent, directed forward. Umbonal region gibbous, sub- 

 tending an angle of about 90°. 



Wing large, triangular, not distinctly defined, margin rounded, with a 

 gentle concavity near the junction of the valve. Ear not observed. 



Test thick, marked by distant, strong radii from the umbo to the base ; 

 the interspaces having alternating larger and smaller rays ; crossed by con- 

 centric, undulating lamellose striae of growth. 



Interior unknown. 



The specimen has a length of 120 mm., height 100 mm., and the hinge- 

 line, from the beak to the extremity of the wing, 95 mm. 



This species is distinguished by its large size, very distant strong radii, and 

 convexity. Compared with P. jiabella, it is proportionally longer, and the wing 

 less defined. Compared with P. pinguis, it differs in greater length and some- 

 what less gibbosity. 



Formation and locality. In the upper Helderberg limestone, in Scott Co., 

 Indiana. 



