LAMELLIBRANCHIATA. 237 



PTERONITES, McCoy. 

 Pteronites profundus. 



PLATE XXII, FIGS. 25, 26, 27. 



Pteronites ■prafimdm. Hai.l. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 22, figs. 25-27. 



Jan., 1883. 



Shell large, lougitudinally semi-ovate ; body semi-elliptical, arcuate, oblique 

 to the hinge-line at an angle of about 30° ; length about twice the height ; 

 anterior margin very oblique, slightly concave beneath the beak and gradu- 

 ally curving into the broadly rounded basal margin; posterior margin 

 obliquely truncate, slightly curving below. 



Left valve convex in the lower part, gibbous from the middle upwards. 

 Right valve unknown. 



Hinge-line straight ; length more than the greatest length of the shell. 



Beak sub-anterior, obtuse, rising but little above the hinge-line, and 

 apparently not incurved. Umbonal region very gibbous, subtending an acute 

 angle. 



Anterior end produced into an acute extension which is limited by a very 

 shallow byssal depression. Wing not defined, extending from the beak the 

 entire length of the shell, and produced beyond the posterior extremity of 

 the body ; margin very slightly concave, extending at nearly right angles to 

 the axis of the body. 



Test of moderate thickness, marked by concentric striae. The casts show 

 distant, irregular, concentric undulations. 



Hinge with a single continuous groove. The pallial line extends parallel 

 to the ventral margin, from a point anterior to the beak to below the middle 

 of the length of the body. 



A large left valve has a length of 78 mm., with a height of 38 mm., and 

 hinge-line 90 mm. A smaller example has a length of 37 mm., height 

 23 mm., and hinge-line 40 mm. 



