LAMELLIBRANCHIA TA. 
319 
Nucula varicosa. 
PLATE XLVI, FIGS. 12-23; AND PLATE XCIII, FIG. 4. 
Nucula varicosa, 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. 
Yalves gibbous, ventricose in the innbonal 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 striae, 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 corbuliformis. 
PLATE XLVI, FIGS. (10, 11 ?), 24-34 (35, 36, 37 ?). 
Nucula corbulifcmnis, Hall. Prelim. Notice Lamellibranchiata, 2, p. 2. 1870. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 46, fig-s. 24-37. 
Shell of medium size, or smaller, broadly triangular, sub-ovate; length about 
one-fourth greater than the height; basal margin broadly curving, more 
