24 
BULLETIN OF THE LABORATORIES 
ears produced upward so that the hinge line is straight and distant 
from the groves, while on the right valve the ridge is at the upper 
margin. Thus Prof. Hall has compared the hinge line of a right valve 
of Pernopecten limiformis with the left valve of P. shumardianus on 
Plate I, of the Report of the State Geologist of New York. The pro- 
jecting ears of the left valve evidently prevent the easy dis-articulation 
of the valves in this monomuscular form perhaps especially liable to 
such an accident. 
Shell very thin, compressed, very ineqi-valve, height of left valve 
noticeably greater than width; general outline (without the ears) 
acutely oval, lower outline a nearly regular curve, extending posteri- 
orly about one third the height of the shell, anteriorly two-thirds 
the height, posterior margin thence proceeding upward nearly 
a straight but oblique line to the angle of the ear, but rather 
abruptly angled near the union of the upper and middle thirds 
of the height, the anterior margin is strongly curved inward 
at the same point and thence continued in a . line at about 
the same angle as the opposite side to the ears, which pro- 
ject slightly upward so that the angles formed by the hinge line 
and the lateral margins are about right angles ; position of the hinge 
of the opposite valve indicated by an impressed groove appearing out- 
wardly as a ridge; ears set off by distinctly marked furrows ; ■ valve 
marked by numerous faint concentric lines and very feeble distant ra- 
diating striations. 
Right valve as high as wide, its lower margin qvenly rounded, 
the curve continuing on both sides to nearly yi the height, the front 
side more produced and abruptly curved, front ear longer but less high, 
so that the hinge line, which is nearly straight, seems oblique to the 
long axis of the valve. 
Entolium atteniiatuin, sp. n. 
(Plate I, Fig. 1 1, ) 
A very slender species represented by a single left valve is derived 
from the flinty limestone at the top of Flint Ridge, and thus loo feet 
higher than the horizon of the above named. This species was much 
more elongated, and had a very narrow hinge. The lower margin is 
uniformly but strongly curved, while the sides are nearly straight and 
inclined at a very acute angle to each other. The anterior margin 
