LAMELLIBRANCHIA TA. 
405 
above the hinge-line. Umbonal slope distinctly angular, extending to the 
post-inferior extremity. Post-cardinal slope flat or convex, with an obscure 
fold along the middle, which may be obsolete in the cast. Cincture not 
conspicuous, consisting of a slight depression or constriction extending from 
the beaks obliquely backward to about the middle of the shell. 
Surface marked by fine concentric stria?, which become fascicled, produc¬ 
ing low undulations, which are usually more conspicuous on the anterior and 
posterior portions of the shell; also obscurely marked, in the cast, by fine 
radiating striae posterior to the cincture. Interior unknown. 
Three specimens measure respectively 50, 44 and 37 mm. in length, and 
22, 20 and 16 mm. in height. 
This species closely resembles S. rigidus, but the cincture is more oblique, 
extending further backward on the basal margin; the post-cardinal slope is 
narrower and less distinctly marked by a fold along the middle. 
Formation and locality. In the Waverly sandstone, at Newark, 0. 
Spiienotus signatus, n. sp. 
PLATE XCIV, FIG. 3. 
Shell large, very elongate-elliptical; length nearly three times the height; 
basal margin gently curving. Posterior extremity doubly truncate, vertical 
below and oblique above. - Cardinal line long, very gently arcuate. Ante¬ 
rior end produced, declining from the beaks and narrowly rounded. 
Valves moderately convex along the basal and posterior portions, becom¬ 
ing gibbous in the middle. 
Beaks sub-anterior, small, but little elevated above the hinge. Umbonal 
ridge rounded, scarcely angular, extending to the post-inferior extremity. 
A sub-angular fold extends along the middle of the post-cardinal slope. 
Surface marked by fine concentric striae, which are distinctly undulated 
in passing over the umbonal and cardinal ridges. 
The specimen described has a length of 55 mm. and a height of 20 mm. 
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