40 PROCEEDINGS OF THE NATIONAL MUSEUM. vor.54. 



furrow extending from the middle of the shell to the basal margin, 

 The post-cardinal slope is abrupt as is also that at the front end of 

 the shell. The surface is marked by fine concentric stria and stronger 

 lines of growth about two milhmeters apart. The clavicle is slender, 

 runs about half way to the base, and is directed backward at about 

 40 degrees from the hinge line. 



Formation and locallhj. — Pembroke formation, splintery gray 

 shales, in the southern part of West Pembroke, on west side Penna- 

 maquam River (loc. No. 1.45.6 A). 



Type-specimen.— Csit. No. 62882, U.S.N.M. 



NUCULITES ATREUS, new species. 



Plate 12, fig. 3. 



The name, Nuculites atreus, is given to a transversely elliptical shell, 

 the beak of which is situated almost central (about 1 mm, in front of 

 the center). The valves moderately convex, beak low, protruding 

 slightly beyond the hinge margin. The two ends are sub-equal, the 

 anterior evenly rounded, the posterior obliquely truncated, forming a 

 blunt angle with the base line. The umbonal ridge is only shghtly 

 angular, scarcely separating the body lope from the post-umbonal 

 slope. The hinge line is shghtly arching, corresponding to the gentle 

 curvature of the basal margin, making the form nearly equilateral. 

 The clavicle is thin and reaches less than half way to the basal margin, 

 and inclines forward about 35° from a transverse line running through 

 the middle of the shell. There are distinct crenulations on the hinge. 

 The surface markings are as upon N. chrysippus. 



The surface of this shell is evenly rounded from front to the umbo- 

 nal angle, which is only slightly and broadly undulate. There are 

 no indications of furrows or ridges radiating from the beak, and the 

 only break in this even curvature of the margin is the posterior 

 truncation spanning the end of the slope between the umbonal ridge 

 and the end of the hinge line. 



The shell presents some resemblance in outer form to Palaeoneilo 

 plana Hall, and may be distinguished from Hall's figure (24 of plate 

 48) by the more central position of its beak, the broader curvature 

 of the anterior end, and the wider and truncate termination of the 

 posterior end. In addition to the crenulate teeth of Palaeoneilo, this 

 species has the clavicle of Nuculites. Dimensions: antero-posterior 

 diameter 18 mm., height from beak to basal margin, 7 mm. (=39 

 per cent). The beak is 8^ mm. from front and 9^ mm. from posterior 

 extremity. 



Formation and locality. — Pembroke formation, splintery gray shales 

 in the southern part of West Pembroke on west side of Pennamaquam 

 River (loc. No. 1.45.6 A). 



Type-specimen.— Cd.t. No. 62883, U.S.N.M. 



