480 PALEONTOLOGY OF NEW YORK. 



the posterior margin. The unibonal angle and principal cardinal ridge arc 

 about equal in length and prominence. 



Surface marked by fine concentric striae which are fasciculate on the body 

 of the shell and produce gentle undulations. The stria3 on the cardinal slope 

 and plications are sharply undulated and not fasciculate. 



Three specimens measure respectively 25, 34 and 40 mm. in length, and 4, 

 4 and 6 mm. in height. 



This species is much smaller and proportionally more elongate than 0. undulala 

 and is distinguished by the carinas on the post-cardinal slope and absence of 

 vertical undulations. 



Formation and localities. In the shales of the Hamilton group at Vinegar- 

 brook glen, Norton's landing, Cayuga lake ; at Earlville, Madison county ; and 

 in Schoharie county. The original locality cited by Mr. Conrad is at Tinker's 

 falls, Onondaga county, N. Y. 



OrTHONOTA ENSIFOHMIS. 



PLATE LXXVIU, FIG. 36. 



Orthonota enxifirrmig. Hall. Prelim. Notice Lamellibranchiatii, 2, \>. 89. 1870. 



Pal. N. Y., vol. V, pt. 1. Plates ami KxplanatioiKs: PI. 78, fig. 3t). 1883. 



Shell small, ensiform, sub-cylindrical ; length eight times the height ; basal 

 margin gently curving for the entire length of the shell. Posterior extrem- 

 ity obliquely truncate. Cardinal line concave, parallel to the basal margin, 

 extending nearly the entire length of the shell. Anterior end short and 

 narrowly rounded. 



Valves of regular convexity throughout. 



Beaks sub-anterior, inconspicuous. Umbonal slope indicated by a slender, 

 low ridge, extending to the post-inferior extremity. Post-cardinal slope 

 marked by a low, angular ridge, which is more conspicuous along the poste- 

 rior half of the shell. 



Surface marked by fine, regular concentric strijE, which are abruptly bent 

 upward at the umbonal angle and undulated on crossing the post-cardinal 

 ridge. 



