322 PALEONTOLOGY OF NEW YORK. 



The specimen has a length of 21 mm., height 18 mm. and a depth to both 

 valves of 14 mm. 



This species is distinguished by its broadly ovate form, very prominent 

 umbones and short anterior end. 



Formation and locality. In the Chemung group, at Mansfield, Pa. 



NUCULA DIFFIDENS, n. Sp. 



PLATE XLV, FIGS. 12, M. 



In part Nuetila RandaUi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 45, figs. 5-16. 



1883. 



Shell of about medium size ; narrowly ovate ; length less than twice the 

 height; basal margin less curved toward the anterior and more curved 

 toward the posterior. Posterior extremity narrowly rounded. Cardinal line 

 declining posteriorly. Anterior end short, and abruptly rounded below. 



Valves gibbous in the middle and above. 



Beaks at the anterior third, prominent. Umbonal slope obtusely sub- 

 angular, merging into the general convexity of the valve before reaching 

 the posterior margin. 



Surface marked by fine concentric striae, which are often irregularly 

 fasciculate, especially toward the margin. Muscular impressions strongly 

 marked. Teeth well developed. 



Three specimens measure respectively 19, 17 and 16 mm. in length, and 

 11, 10 and 9 mm. in height. 



This species resembles some of the smaller forms of N. RandaUi, but the 

 posterior end is wider, beaks less elevated and the umbonal slope is not so 

 strongly defined. 



Formation and localities. In the shales of the lower Chemung group at Ithaca, 

 and in Chemung county, N. Y. 



NuCULA OLOBULARIS, n. Sp. 

 PLATE XCni, FIG. 6. 



Shell robust, of medium size ; sub-globose ; length somewhat greater than the 

 height ; basal margin regularly rounded, abruptly curving at both extrem- 



