112 PALEONTOLOGY OF NEW-YORK. 
148. 11. LEPTASNA PLANUMBONA (n. sp.). 
Pu. XXXI. B. Figs. 4 a, b,c, d, e. 
Shell resupinate, robust, length and breadth as 9 to 11; cardinal line straight, suddenly 
deflected at the extremities, equal to or greater than the width of the shell; sides a little 
contracted just below the cardinal extremities, leaving slightly salient angles ; ventral valve 
flat or slightly depressed near the beak, elevated and very convex in the middle, somewhat 
abruptly and concentrically deflected towards the margin; dorsal valve flat on the disc, 
slightly elevated towards the beak, and deflected to correspond with the other valve ; 
surface marked by radiating strie, every third, fourth or fifth of which is alternated by a 
stronger one; entire surface (in perfect specimens) marked by fine concentric elevated 
lines, and a few imbricating lines of growth. 
This is a very neat symmetrical species, presenting very little variation of form. The 
concentric lines are often obliterated, and the surface shows only the radiating strie. The 
remarkable flatness, which often amounts almost to a depression of the convex valve near 
the beak, is a distinguishing character in all the specimens I have examined. The sides 
of the shell are suddenly constricted just below the extremities of the hinge line, producing 
small salient ears; the ventral valve is very convex just forward of the middle, and the 
opposite valve equally concave. 
Fig. 4.4 & b. Views of the two valves; the ventral or convex one 6 showing some strong imbricating 
lines of growth, while the other valve has but a single one. The beak of the dorsal valve 
projects beyond the cardinal line of the other valve, as shown in 4 8, 
Fig. 4c. Cardinal view, showing the nearly linear area and closed foramen. There is sometimes a small 
space for the protrusion of the ligament. 
Fig. 4 d. Interior of the concave valve, showing the visceral impression, which is nearly circular, 
depressed in the centre, and longitudinally marked by strong elevated ridges; it is margined 
by an elevated border, which proceeds from the two extremities of the foramen, and, curving 
around, leaves a narrow slit in front. There is an elevated line extending from the beak of 
the shell, through this slit, to the centre of the valve. The margin is marked by strong ribs, 
which reach from the edge to the point of curvature of the shell; these ribs are produced 
by the elevated strie on the outside, which leave a depression upon the inner margin. 
Fig. 4 e. Lateral view of the shell, showing its convexity in the middle, and flattening towards the beak. 
Position and locality. This shell has not been very clearly recognized in New-York, but 
it is abundant at the West, in the Blue limestone, holding a position equivalent to that of 
the Trenton limestone, and associated with the preceding species of Leprmna. Among the 
western localities, I may mention Cincinnati and Oxford (Ohio) , Madison ( Indiana), and 
Maysville ( Kentucky). (State Collection.) 
