74 
BULLETIN OF THE LABORATORIES 
Allorisina convexa, sp. n. 
(Plate XII, Fig. 27.) 
Shell of medium size, quite tumid, with parallel margins and nu- 
merous fine striae. Length nearly 2^ times the height; hinge and 
lower margins parallel and of equal length ; lower margin abruptly 
rounded to the middle of the height, passing sharply into the concave 
antero-dorsal line; lunette well defined; posterior margin broadly 
rounded with slight angulation at the termini of two faint ridges be- 
tween the post-umbonal ridge and the hinge; surface highest near the 
middle, flattened postero-dorsally ; post umbonal ridge faint, the supra- 
umbonal ridges inconspicuous, but producing slight deviation in the 
numerous and regular concentric stri^. The ca§t shows a long cardi- 
nal groove. This shell is some respects a miniature of A. nobilis, but 
is much more convex. The radiating striae characteristic of Allorisma 
may be detected upon the cast. From A. winchelli, which it exactly 
resembles in size, it may be distinguished by the parallel sides and the 
form of the posterior margin. From all other forms of this age it will 
readily be distinguished. Length 57 mm ; height 23 mm ; beak from 
the front 10 mm ; convexity of both valves about 15 mm. Free stone 
layers of middle Waverly^ 6 miles northwest of Granville. Collected 
by W. F. Cooper. 
Macrodon ? ? triangularis , sp. n. 
(Plate VIII, Fig. 8.) 
A single right valve differs so from all associated forms that very 
little idea is afforded of its relations. 
Shell thick, nuculiform, large; outline subtriangular, beaks rather 
prominent, somewhat incurved ; hinge apparently flexed at nearly a 
right angle at the beak, anterior margin nearly straight, meeting the 
gently curved lower margin by an abrupt curve; posterior margin 
very short, forming an acute angle with the lower margin and a very 
obtuse one with the curved hinge line; post umbonal slope narrow, 
inclined to the general surface of the valve at nearly a right angle ; 
surface marked by concentric striae and folds ; greatest convexity 
