lameijjbranchia ta. 
401 
Post-cardinal slope broad. Cincture extending from the beak obliquely to 
the base, becoming broad below the middle of the shell. 
Surface marked by fine concentric strirn, the impressions of which are 
preserved upon the cast. 
Anterior muscular impression deeply marked, limited posteriorly by a 
ridge, situated just below the beaks. Pallial line continued parallel to the 
basal margin, recurving over the umbonal ridge and terminating in a large 
muscular scar on the post-cardinal slope. 
The specimen described has a length of 50 mm. and a height of 23 mm. 
This species somewhat resembles S. subtortuosus, but the umbonal ridge is 
more arcuate, the cardinal slope is wider and without distinct plication. 
Formution and locality. In a conglomerate of the Chemung group, east of 
Panama, N. Y. 
Sphenotus clavulus. 
ELATE LXVI, FIGS. 2, 20-20. 
Sangidnolites ? clavulus, Hall. Prelim. Notice Lamellibranchiata, 2, p. 45. 1870. 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates arid Explanations: PI. 66, figs. 20-26. 1883. 
Shell of medium or large size, elongate, sub-trapezoidal; length more than 
two and a half times the height; basal margin nearly straight or slightly 
arcuate in the middle, curving to the anterior and posterior extremities. 
Posterior extremity narrowly rounded below and oblique above. Cardinal 
line straight, slightly declining posteriorly, nearly parallel to the basal mar¬ 
gin and extending more than half the length of the shell. Anterior end 
declining more or less abruptly from the beaks and narrowly rounded below. 
Valves moderately convex below, gibbous in the middle, and on the umbo¬ 
nal slope to beyond the middle of its length. 
Beaks sub-anterior, small, closely appressed, incurved, and rising very 
little above the hinge. Umbonal slope sub-angular from the beak to the 
middle of its length, becoming rounded and less defined below and reaching 
the post-inferior extremity. Post-cardinal slope moderately convex, with 
