LAMELLIBRANCHIA TA. 
323 
ities; posterior end regularly rounded. Cardinal margin declining on both 
sides of the beak. Anterior end abruptly rounded below. 
Valves ventricose. 
Beaks at about the anterior third, rounded, incurved. Umbonal region 
very gibbous. Umbonal slope not defined, rounded. 
Surface marked by regular, sharp, concentric stria; with a few varices of 
growth. Interior unknown. 
A specimen has a length of 20 mm. and a height of 17 mm. 
This species somewhat resembles, in outline, N. bellistriota, but it is more 
ventricose, the beaks more erect and the umbonal slope is less defined. 
Formation and localities. In a conglomerate of the Chemung group, associated 
with Ptychopteria Sao and Spirifera Verneuili, east of Panama, N. Y., and at 
Warren, Pa. 
Nucula Houghtoni. 
PLATE XLV, FIGS. 29-31. 
Nucula Houghtoni, Stevens. Am. Jour. Sci., 2d series, vol. 25, p. 262. 185S. 
Nucula Iowensis, White and Whitfield. Proc. Bost. Soc. Nat. Hist., vol. S. 1S62. 
“ “ Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 45, figs. 29-31. 1883. 
Shell of medium size, ovate, sub-trigonal; length more than one-fourth greater 
than the height; basal margin broadly curving, abruptly rounding into both 
extremities. Cardinal line sloping rapidly from the beaks to the anterior 
and posterior extremities. Anterior end short, declining rapidly from the 
beaks and abruptly rounded below. 
Valves gibbous, ventricose in the umbonal region. 
Beaks at about the anterior fourth, prominent, arching over the hinge-line. 
Umbo prominent. Umbonal slope defined, rounded, extending from the beak 
to the posterior extremity of the shell. 
Test strong, marked by very fine concentric striae which are scarcely fas¬ 
ciculate on the body of the shell. 
There are about ten strong teeth posterior to the cartilage pit, and five 
anterior ones. Muscular scars strongly impressed. 
