114 PALEONTOLOGY OF NEW-YORK. 
Fig. 6 a. View of ventral valve. 
Fig. 6 4. Cardinal view of the same shell. 
Position and locality. Associated with the last species, and others, in the lower shaly 
limestone at Mineral Point ( Wisconsin). : 
151. 14. LEPTAXNA PLANOCONVEXA (n. sp.). 
Pi. XXXI. B. Figs. 7 a, b, ¢, d. 
Shell resupinate, sub-planoconvex, often distinctly inequilateral and oblique; ventral 
valve moderately convex; dorsal valve nearly flat or slightly concave; cardinal line 
extended considerably beyond the width of the shell, and often preduced into small acute 
ears ; surface marked by rather coarse radiating strie, which bifurcate towards the margin 
of the shell ; apex usually, and perhaps always, perforated ; foramen closed; cardinal 
area narrow. 
The most obvious characters of this shell are its resupinate form, the nearly flat dorsal 
valve, and frequent inequality of the two sides, or the greater extension of the cardinal line 
on one side. In these features alone it is dissimilar to all the other species of the genus in 
the lower strata. In its nearly flat valve, it approaches to the Orruis; while the extension 
of the cardinal line, and closed foramen, are characters belonging to Leprmna, as well, 
also, as its general habit, which is different from the true Orruts. 
In some of its varieties, and particularly in the ventral valve being flat near the beak, it 
resembles the last species, but differs essentially from it in the coarser nearly equal strie 
and absence of concentric elevated lines, as well as other important characters. 
Fig. 7 a. View of the dorsal valve, with one of the cardinal extremities produced beyond the other ; this 
feature is not due to wearing, but is the natural form of the shell. 
Fig. 7 6. View of a smaller specimen, more nearly equilateral. 
Fig. 7 c, Profile view of the shell. 
Fig. 7 d. Cardinal view of the first specimen. 
Position and locality. This species occurs associated with the two last, having a very 
extensive geographical range. It is known in numerous localities in Ohio, Indiana, Ken- 
tucky and Wisconsin. (State Collection.) 
