tJTICA SLATE AND HUDSON-RIVER GROUP. 299 



This species is very distinctly characterized by tlie ol)lique impression or sinus, wliirh 

 produces an indentation in the basal inarj^in, and often leaves the posterior extremity 

 acute. 



iPig. 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 mctamorphic slates of Waterford, Saratoga county. 



357. 1. ORTHONOTA PHOLADIS. 



Pl. LXXXII. Fig. 6. ■ . - 



Pterinea pholadis. Conrad, Ann. Geol. Report, 1S3S, p. 118. 

 Orthonota pholadis. Id. lb. 18J1, p. 151. 



" 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 i\Ir. 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 (ji.i/j.). 



Pl. LXXXII. Figs. 7 a, ft, 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 obliquelj' towards, l)ut not reaching, the 

 posterior basal margin ; surface marked by fine concentric stria;, and a few obli(|ue 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 e. The left side of a cast scarcely retaining any markings. 

 Fig. 7 d. Dorsal view of the same. The anterior extremity is partially eroded. 



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