318 PALEONTOLOGY OF NEW YORK. 



NUCULA BELLISTRIATA. 



PLATE XLVI, FIGS. 1-9. 



NucuiUes beUaatrUtta, Cokrad. Geol. Sui-v. N. Y., Ann. Rep., p. 40. 1841. 



Nucula beUaatriata (Conrad), Hall. Pi-elim. Notice Lamellibianchiata, 2, p. 2. 1870. 



.< «" " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations: PI. 4(5, tigs. 



1-11. 1883. 



Shell of medium size, broadly ovate, usually somewhat wider behind ; length 

 about one-fourth greater than the height ; basal margin regularly curving. 

 Posterior end broad and rounded. Cardinal line oblique and arcuate. Ante- 

 rior end short, declining rapidly from the beaks, and abruptly rounded below. 



Valves convex, gibbous on the umbo. 



Beaks, at about the anterior fourth, appressed, rising above the hinge-line, 

 directed forward. Umbonal slope rounded, extending from the beaks in an 

 arching direction, to above the post-basal extremity. 



Surface marked by fine, regular, sharp, concentric strias, which do not 

 appear to be aggregated into fascicles, but are sometimes interrupted, and the 

 surface undulated by strong varices of growth. 



The cast of the interior shows the strong muscular impressions and a 

 broad, thickened hinge. 



Three specimens measure respectively 21, 17 and 16 mm. in length, and 

 14, 13 and 12.5 mm. in height. 



The distinguishing chariicters of this species are its broad and sub-circular 

 form and regular concentric striae. In some of its phases it resembles N. vari- 

 cosa, but that species is sub-trigonal in outline, with larger incurved beaks, and 

 the striae are fasciculate, forming strong undulations of the surface at irregular 

 intervals. It is less gibbous and broader than N. Randalli, the striae are finer, 

 usually without varices of growth, and the beaks more appressed and directed 

 forward. 



Formation and localities. In the shales of the Hamilton group, in Schoharie 

 county ; near Smnyra, Chenango county ; at numerous localities in Onondaga 

 county, and on the shores of Seneca, Cayuga and Canandaigua lakes, N. Y. 



