LAMELLIBRANCHIATA. 317 



This species is readily distinguished from any of the associated species by the 

 strongly Urate surface. It differs also from JV. Randalli in its surface strise, 

 lesser gibbosity and more distant beaks. 



Formation and localities. In the shales of the Hamilton group, on the shores 

 of Skaneateles, Cayuga and Seneca lakes, N. Y. 



NUCUL-A. SUBELLIPTICA. 



PLATE XLV, FIG. 28. 



NucuXa subelliplica. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 45, fig. 28, 1883. 



Shell large, ovate, wider behind ; length about one-fourth greater than the 

 height ; basal margin regularly rounded, abruptly curving into the anterior 

 end. Posterior end rounded. Cardinal line slightly arcuate. Anterior end 

 short and abruptly rounded. 



Valves convex, gibbous in the middle and on the umbonal region. 



Beaks sub-anterior, prominent, rising above the hinge-line. Umbo gib- 

 bous. Umbonal slope I'ounded, becoming obsolete before reaching the post- 

 basal extremity. 



Test and surface markings not observed. 



The specimen is a cast of the interior, showing strong muscular scars and 

 the remains of very numerous and small post-cardinal teeth. 

 • The internal mould has a length of 27 mm., and a height of 20 mm., with 

 a depth to both valves of about 15 mm. 



This species is distinguished from others of the horizon of the Hamilton 

 group, in its regular ovate form, which is broader behind, and by its rounded 

 umbonal slope. It somewhat resembles certain forms of N. bellistriata , but it is 

 a larger shell, more elongate in outline, with more prominent beaks and more 

 numerous hinge-teeth. 



Formation and locality. In the shales of the Hamilton group, near Cumber- 

 land, Md, 



41 



