LAMELLIBRANCHIATA. 503 



Test thin, marked by fine, regular concentric striae, which become crowded 

 on the anterior end and sometimes fasciculate on the body of the shell. 

 Interior unknown. 



A medium-sized specimen has a length of 14 mm. and height of 8 mm. 

 A larger specimen measures 15 mm. in length and 9 mm. in height. 



This species is distinguished by its small size, regularly curving base, and 

 symmetrical posterior extremity. 



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

 shores of Seneca and Cayuga lakes. 



Elymella nuculoides, n. sp. 



PLATE XL, FIOJS. 6, 7, S, 10? 



In piirt ModUnnorpha 1 liyalea. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 40, figs. 



5-11. 1883. 

 Not " " " Prelim. Notice Laraellibranchiata, 2, p. 79. 1870. 



Shell small, broad, obliquely ovate ; length more than one-half greater than 

 the height ; basal margin regularly curving, more abruptly recurving at the 

 anterior end ; posterior margin regularly rounded, recurving into the cardi- 

 nal line, which is straight for half its length. Anterior end short, regularly 

 rounded. 



Valves moderately convex on the posterior and ventral portions, becoming 

 gibbous in the middle and umbonal regions. 



Hinge-line straight, extending a little less than half the length of the shell. 



Beaks anterior, prominent and incurved, rising little above the hinge-line. 

 Umbonal region regularly gibbous, without defined ridge. When the shell 

 is partially compressed, it develops an undefined ridge in the line of the 

 umbonal slope. 



Test moderately thick, marked by fine concentric striae which are fascicu- 

 late on the body of the shell, giving rise to strong undulations. Interior 

 unknown. 



A medium-sized specimen has a length of 28 mm. and a height of 17 mm. 

 A larger individual measures 30 mm. in length and 18 mm. in height. 



