H 

 124 PALAEONTOLOGY OF NEW-YORK. 



165. 12. ORTHIS PECTINELLA, var. SEMIOVALIS. 

 Pl. XXXII. Figs. 11 a, 6, c. 



Bioatlly 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. pedinella in its greater proportionate width 

 and finer plications, though not sufficiently to make it a distinct species. It approaches 

 somewhat in shape to the 0. piicatella, 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. 1 1. A large specimen, somewhat imperfect on one side. The plications in this shell are 36. 



Fig. 11 a, b. Dorsal and ventral valve of a smaller individual, the latter somewhat worn on the surface. 



Position and locality. In the higher part of the Trenton limestone at Turin, Watertown, 

 and Middle ville. (State Collection.) 



* I 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 ditTerence 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 venti'al valve, in t}ie European specimen, is readily contrasted with the 

 short beak of the convex valve in O. pcctintUa ; while the dorsal valve, nearly fiat on the centre, is elevated at the 

 bealc, producing the area. 



The species known in Ohio as O. ca/laclis {O. piicatella, p. 122), is quite distinct from the European species of 

 that name, as will be readily seen on comparison of figs. H a - h, Plate xxxii. 



Fig. a. View of the ventral valve of Oitliis calligramma. 



Fig. b. Profile view of the same. 



Fig. c. Profile view of Ort/iis pectinella. 



