162 PALEOZOIC PALEONTOLOGY. 
The dimensions of an average specimen are: length, 3.5 mm.; 
breadth, 2.8 mm.; thickness 1.8 mm. 
Remarks.—This interesting species has hitherto been recorded only 
from the Mississippi valley. The New Jersey specimens are indis- 
tinguishable from the western ones, but are somewhat smaller, the 
largest specimen observed being less than 5 mm. in length. In the 
eastern specimens the faint marginal plications, which are present in 
the larger western individuals, have not been observed. 
MOLLUSCA. 
PELECYPODA. 
CUNEAMYA TRUNCATULA Ul. 
Plate XI., Fig. 6. 
189%. Cuneamya truncatula Ulr., Pal. Minn., pt. I, p. 622, pl. 36, 
fig. 39. 
Description —‘Shell of medium size, transversely somewhat elon- 
gate, the two ends of nearly equal height, with broad, compressed, 
nearly terminal, prominent and incurved beaks; postero-cardinal 
region subalate, escutcheon less than half the length of the hinge. 
Cardinal and basal margins diverging shghtly posteriorly; anterior 
end truncate, almost vertical, the upper two-thirds sharply inflected, 
forming a rather narrow, deep and unusually long lunule, from 
whose lower end the outline slopes abruptly backwards into the 
basal line; the latter is gently convex in the posterior half, straight 
or very slightly sinuate in front of the middle, very obtusely angular 
in the anterior third, and straight again when it ascends from the 
anterior basal angle to the lower extremity of the lunule; posterior 
margin somewhat produced and strongly rounded in the lower half, 
and very obliquely subtruncate in the upper. Posterior umbonal ridge 
rather prominent, strongly rounded, not angular, curved and becoming 
almost obsolete in the posterior third of the shell; cardinal slope con- 
cave, very abrupt near the beaks; a narrow, but distinct, anterior 
umbonal ridge descends at right angles to the hinge-line from the 
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