338 PALAEONTOLOGY OF NEW YORK. 



striaj, while in that species the same character of surfjice affects only the poste- 

 rior half of the shell. 



In form and proportions, the three species, P. tenuistriata, P. fecunda and P. 

 muta, are very similar, and might be included under one specific designation, 

 except for the wide and characteristic differences in the surface ornamentation, 

 which are constant even among specimens from the same locality. 



Formation and localities. In the soft shales of the Hamilton group, on the 

 shores of Skaneateles, Seneca and Canandaigua lakes ; at North Bristol, in Onta- 

 rio county ; at Bellona, Yates county, and other localities in Western N. Y. 

 It likewise occurs in the same formation in Hardy county, Va. 



Pal^oneilo emarginata. 



PLATE L, FIGS. 1-11. 



NuculUes emarginata, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 50. 1841. 



Palceonello emarginaia (Conrad), Hall. Prelim. Notice Lamellibranchiata, 2, \i. 7. 1870. 



" " " " Pal. N. Y., vol. V, pt, 1. Plates and Explanations: PI. 50, figs. 



1-12. 1883. 



Shell of medium size or larger, sub-elliptical ; length usually more than twice the 

 height; basal margin gently curving or nearly straight from the post-inferior 

 angle to the anterior end, where it is more abruptly rounded ; posterior margin 

 deeply sinuate. Cardinal line gently arcuate. Anterior end regidarly and 

 somewhat abruptly rounded. 



Valves regularly convex in the lower anterior half, becoming gibbous 

 above. 



Beaks at a little less than the anterior third from the end, and, except 

 in the shorter forms, moderately prominent. Umbonal slope marked by a 

 strong elevation or ridge, with a depression above it, which produces a 

 marked emargination. The post-cardinal extremity, above this, is produced 

 into a linguiform extension, which is sometimes angular, but usually abruptly 

 rounded at the termination. 



Surface marked by strong, elevated, distant, lamellose, concentric ridges, 

 extending the entire length of the shell, between which are very fine con- 



