Foerste.] 
324 
[May 1, 
and the postero-lateral angles and the general form are more like 
var. Salterii but with the angles nearer a right angle. In one spec- 
imen, at a distance of 17 mm. from the beak, the shell bends down- 
wards for 1 mm. and then outwards at an angle of 15° to its former 
course, thus increasing the convexity of the shell. There is no in- 
dication of a mesial depression or fold. The dental lamellae in a 
finely preserved specimen are seen to project into the shell, form- 
ing a small angle with each other. They are flattened above, and 
medially show the impression of a narrow groove. Within 2 mm. 
of the dental lamellae are two muscular impressions divided by a 
narrow ridge. The muscular impressions or scars are sharply de- 
fined posteriorly but become indistinct after a length of 3 mm., as 
does also the dividing ridge. These scars are the most variable 
feature of the shell and may often be entirely obsolete, all inter- 
mediate stages being found. For the present we designate these 
flattened specimens as Stricklandinia lens var. planus , although if 
our interpretation of them be correct they perhaps belong more cor- 
rectly to variety melissa, which also seems to be destitute of mesial 
fold and sinus. 
Pentamerus ovalis, Hall. 
(PLATE V, FIGS. 17, 18.) 
This species was described by Hall from the Clinton Group of 
New York. 
Specimens were found at Cumberland Gap, Tennessee, which we 
place under this species. They certainly do not bear the closest 
resemblance to the published figures of that species ; but no direct 
comparison with the New York specimens having been made, we 
are not prepared to pronounce them distinct. The best preserved 
specimen is 17 mm. broad and long. A dorsal valve is 21.3 mm. 
broad and long. One ventral valve may have had a faint mesial 
fold, but is imperfect anteriorly. 
This same form is very common at Collinsville, Alabama, and 
from the specimens here found the following description is pre- 
pared. 
Shell small, our specimens not exceeding 22 mm. in length and 
breadth. Both valves moderately convex in general, the ventral 
valve strongly convex at the beak. The beak of the casts of the 
dorsal valve scarcely distinct, that of the ventral valve far more 
