124 PALEONTOLOGY OF NEW-YORK. 
165., 12. ORTHIS PECTINELLA, var. SEMIOVALIS. 
Pu. XXXII. Figs. 11 a, 8, ¢. 
Broadly semioval, resupinate, length and breadth as 7 to 10; cardinal line distinct, 
equal to the width of the shell, a little inflected at the extremities ; area moderately broad ; 
dorsal valve depressed-convex near the beak, flat towards the margin, and a little concave 
at the cardinal extremities ; ventral valve regularly convex, with the beak incurved and 
scarcely projecting beyond the margin of the shell; surface marked by about 28 to 36 
simple subangular ribs, with equal intermediate spaces. 
The plications are remarkably simple, showing no tendency to bifurcation, and are 
always clearly defined. It differs from the O. pectinella in its greater proportionate width 
and finer plications, though. not sufficiently to make it a distinct species. It approaches 
somewhat in shape to the O. plicatella, but is usually longer in proportion to its breadth, 
and the sides are more regularly curved. The resupinate character is a strong mark of 
distinction, when the area can be seen.* 
Fig. 11. A large specimen, somewhat imperfect on one side. The plications in this shell are 36. 
Fig. 11 a, &. Dorsal and ventral valve of a smaller individual, the latter somewhat worn on the surface. 
we} 
Position and locality. In the higher part of the Trenton limestone at Turin, Watertown, 
and Middleville. (State Collection.) 
* T have given below two figures of Orthis calligramma, from an authentic European specimen, for the purpose of 
comparison with O. pectinella, which has been regarded as identical with it. The difference in the profile views will 
be at once perceived, as well as in the figure of the ventral valve compared with the figures 10 a and b. The convex 
dorsal valve, with the beak curving over the ventral valve, in the European specimen, is readily contrasted with the 
short beak of the convex valve in O. pectinella ; while the dorsal valve, nearly flat on the centre, is elevated at the 
beak, producing the area. 
The species known in Ohio as O. callactis (O. plicatella, p. 122), is quite distinct from the European species of 
that name, as will be readily seen on comparison of figs. 9 a- A, Plate xxxil. 
Fig. a. View of the ventral valve of Orthis calligramma, 
Fig. 6. Profile view of the same. 
Fig. c. Profile view of Orthis pectinella. 
