MEDINA SANDSTONE. 
11 
392. 18. MODIOLOPSIS? PRIMIGENIUS. ^ ^ , 
yi l < 1 
Unio primigenius. Conrad, Annual Report 1838, p. 113; 1839, p. 66: 
Cypricardia alata. Hall, Geological Report 4th District, pag. 48, fig. 3. 
Subrhomboidal, rounded anteriorly, expanded and alate posteriorly ; hinge-line straight, 
longer than the length of the shell; anterior extremity short; ventral margin rounded ; surface 
marked by strong concentric imbricating lines, which are crossed by fine radiating strife on the 
posterior half of the shell. 
The casts of this shell usually preserve only some remains of the concentric lines, and these 
are sometimes obliterated. In the casts the hinge-line is shorter than the length' of the shell, and 
presents on the anterior slope a fold with a depression on either side, like the impressions pro¬ 
duced by the teeth of the shell. In addition to this, there is a single fold running nearly the 
whole length of the hinge-line, exhibiting in the left valve a well marked depression. The 
surface markings present various degrees of perfection ; and the differences between the entire 
cast and the specimens in different conditions is so great, as to induce a belief that more than 
one species exists ; still I have been unable to distinguish characters in the specimens I have, 
which warrant a separation. 
Fig. 2 a. A small specimen, with the beak very prominent, and almost vertically truncated at 
the posterior extremity. 
Fig. 2 b. A cast having the markings almost entirely obliterated, and showing a fold or depres¬ 
sion along the hinge-line. 
Fig, 2 c. A specimen partially preserving the shell, which is alated on the posterior dorsal mar¬ 
gin, and slightly, acute in front. 
F ig. 2 d. A fragment preserving an impression of the shell, showing the concentric and radiating 
lines. 
Fig, 2 e, A portion of the same enlarged. 
Position and locality. This species occurs at Medina, in a thin stratum charged with uni¬ 
valves, about sixty feet from the surface of the rock. It occurs likewise at Lockport, in the same 
position, or at a less distance below the surface. ( state Collection.) 
*** I am unable to determine the true relations of this shell. It is allied to Modiolopsis, but its 
absolute generic relations may be somewhat different. 
