LAMELLIBRANCHIATA. 319 



NUCULA VARICOSA. 



PLATE XLVI, FIGS. 12-23 ; AND PLATE XCIII, FIG. 4. 



Nucida mricosa. Hall. Prelim. Notice Lamellibranchiata, 2, p. 2. 1870. 



" " " Pal- N. Y., vol. V, pt. 1. Plates and Explanations : PI. 46, figs. 13-23. 1883. 



Shell of medium size, ovate-triangular; length somewhat greater than the 

 height ; basal margin curving, more abruptly rounded posteriorly ; post-car- 

 dinal margin arcuate or sub-truncate. Anterior end very short and abruptly 

 rounded below. 



Valves gibbous, ventricose in the umbonal region. 



Beaks sub-anterior, prominent, incurved, arching over the hinge-line. 

 Umbonal slope narrowly rounded, arching upward and extending from the 

 beaks to the post-basal extremity. Post-cardinal slope narrow. 



Test strong, marked by fine, irregular, concentric stria3, and by numerous 

 varices of growth, which are closely arranged on the marginal portions of 

 the shell. 



Hinge strong, and posterior to the beaks it is marked by a narrow row of 

 very fine transverse teeth. Other characters of the interior unknown. 



Four characteristic specimens measure respectively 18, 17, 16 and 15 mm. 

 in length, and 14, 16, 15 and 12 mm. in height. 



This species is more erect and the beaks much more elevated than in N. belli- 

 striata ; it is higher in proportion to the length, giving a more triangular outline, 

 while the concentric striae are finer, with numerous strong varices of growth. 



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

 of Cayuga lake ; and at Bellona, Yates county, N. Y. 



NuCULA COBBULIFORMIS. 



PLATE XLVI, FIGS. (10, 11 ?), 24-34 (35, 36, 37 ?). 



Nttcula coHmliformis, Hall. Prelim. Notice Lamellibranchiata, 2, p. 2. 1870. 



" " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 46, figs. 24-37. 



Shell of medium size, or smaller, broadly triangular, sub-ov.ate ; length about 

 one-fpurth greater ihm the height; basal margin broadly curving, more 



