UTICA SLATE AND HUDSON-RIVER GROUP. 
299 
This species is very distinctly characterized by the oblique impression or sinus, which 
produces an indentation in the basal margin, and often leaves the posterior extremity 
acute. 
Pig. 5 a. A specimen preserving both valves. 
Fig. 5 b. The right valve, which is less compressed than the preceding. 
Position and locality. This species occurs in the Utica slate, at Turin, associated with 
the Graptolites; in the same position in Montgomery county ; and in the black, glazed, 
and partially metamorphic slates of Waterford, Saratoga county. 
357. 1. ORTHONOTA PHOLADIS. 
Pl. LXXXII. Fig. 6. 
Pterinea pholadis. Conrad, Ann. Geol. Report, 1838, p. 118. 
Orthonota pholadis. Id. Ib. 1841, p. 51. 
u Shell profoundly elongated, ventricose; dorsal and basal margins parallel; posterior 
side rugose, or with short undulations near the dorsal margin. Length If inches.” 
The preceding description is cited from Mr. Conrad, and the figure is also-by him, 
having never seen the shell myself. It resembles the following species, but is much more 
elongated and proportionally narrower. 
Position and locality. In the shales of this group at Pulaski, Oswego county. 
358. 2. ORTHONOTA PARALLEL A (n.sp.). 
Pl. LXXXII. Figs. 7 a, b, c, d. 
Shell extremely elongated and very narrow ; anterior extremity rounded, and contracted 
just forward of the beaks; cardinal margin straight or gently arched; posterior extremity 
rounded, broader than the anterior ; basal margin slightly arcuate ; beaks near the anterior 
extremity having an obscure carina, extending obliquely towards, but not reaching, the 
posterior basal margin; surface marked by fine concentric striae, and a few oblique strong 
wrinkles along the dorsal margin. 
This shell bears considerable resemblance to the 0. pholadis ; but is less extended, and 
has a greater width. The width in this species is fully one third the length, while in the 
figure of 0. pholadis the width is less than one fourth the length. In specimens which are 
imbedded in shale and much compressed, the surface is regularly convex, and the oblique 
elevated carina becomes obsolete. The cast is smooth, with scarcely any evidence of 
the oblique folds on the cardinal margin. 
Fig. 7 a. The left valve, preserving the shell, which is finely striated concentrically, and shows the 
folds upon the cardinal line. 
Fig. 7 b. Dorsal view of a cast in coarse sandstone, where the folds are visible on the dorsal margin. 
Fig. 7 c. The left side of a cast scarcely retaining any markings. 
Fig. 7 d. Dorsal view of the same. The anterior extremity is partially eroded. 
38* 
