480 
PALAEONTOLOGY OF NEW YORK. 
the posterior margin. The umbonal angle and principal cardinal ridge are 
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 striae 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. undulata 
and is distinguished by the carinae 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 ensiformis. 
PLATE LXXVIII, FIG. 36. 
Orthonota ensiformis, -Hall. Prelim. Notice Lamellibranchiata, 2, p. 89. 1870. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 78, fig. 36. 1SS3. 
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 striae, which are abruptly bent 
upward at the umbonal angle and undulated on crossing the post-cardinal 
ridge. 
