4o6 CRETACEOUS PALEONTOLOGY. 



Breviarca cuneata (Gabb). 

 Plate XXX., Fig. 27. 



1876. Trigonarca cuneata Gabb, Proc. Acad. Nat. Sci. Phil.. 



1876, p. 316. 

 1905. Trigonarca cuneata Johns., Proc. Acad. Nat. Sci. Phil., 



1905, p. 9. 



Description. — Shell oblique, subtriangular in outline, the dimen- 

 sions O'f a nearly complete internal cast of a left valve being: 

 length 23 mm., height 18.5 mm., convexity 7.5 mm. Anterior 

 margin rounding from the anterior extremity of the hinge-line 

 into the basal margin, which is gently convex in the central portion, 

 curving upward more abruptly in front and behind ; postero-basal 

 extremity rather sharply rounded; posterior margin obliquely 

 truncate. Valves strongly convex or somewhat ventricose; the 

 beaks, in the casts, rather large and somewhat incurved, elevated 

 above the hinge-line, situated in front of the middle of the shell 

 at about the middle of the hinge-line; umbonal ridge rather 

 sharply rounded, the postero^dorsal slope abrupt ; in front of the 

 umbonal ridge the surface is nearly flat or gently convex for 

 some distance, and then curves rather abruptly to the anterior 

 margin. Hinge-plate with about 12 or 15 teeth on either side 

 of the beak. Surface marked by rather strong concentric lines 

 of growth and by fainter radiating striae. 



Remarks. — This species occurs in the form of internal casts in 

 the Woodbury clay at Lorillard, and can be distinguished from 

 B. saifordi, with which it is associated, by its larger size and 

 by the more conspicuous concentric markings of the shell, shown 

 on impressions of the exterior. These New Jersey examples 

 have been compared with the type and oher authentic specimens 

 from the South, and there seems to be no doubt as to the identity 

 of the species, although their condition of preservation is very 

 different. 



Formation <a<nd locality. — Merchantville clay-marl, near Mat- 

 awan (loi^), near Jamesburg (141); Woodbury clay, Loril- 

 lard (1012). 



Geographic distribution. — New Jersey, Georgia. 



