348 
PALAEONTOLOGY OF NEW YORE 
Valves convex posteriorly and below, becoming gibbous in the middle and 
upper portion. 
Beaks at about the anterior third, prominent, rising but little above 
the hinge-line. Umbonal region regularly convex. Umbonal slope convex 
or sometimes flattened, giving an obscure truncation to the posterior 
extremity. (Fig. 43 exaggerates this feature, which is more properly shown 
in fig. 44.) 
Test thin, marked by fine, close, concentric strim with sharp lamellose 
elevations at irregular intervals. The characters of the interior are shown 
in figs. 45 and 46 of plate 1. 
Three specimens measure respectively 35, 30 and 22 mm. in length, and 
18, 16 and 12 mm. in height. 
This species is more symmetrically ovate and gibbous than any of the pre¬ 
ceding forms. It is easily distinguished from P. attenuata, with which it is 
associated, by its shorter and more gibbous form and absence of mesial con¬ 
striction. 
Its mode of occurrence at Hillsdale, Mich., is in the condition of casts, which 
preserve some impressions of the finer striae, while the place of the stronger 
lamellae is marked by narrow, concentric sulci, suggesting the name given by 
Mr. Conrad. 
A comparison with the type specimens of Leda, nuculiformis, Stevens, leaves no 
doubt of its identity with the species originally described by Mr. Conrad as 
Naculites sulcatma. 
Formation and localities. In the Waverly sandstone at Richfield and Newark, 
0.; also occurring at Battle Creek, and abundantly at Hillsdale, Mich. 
PALiEONEILO ? DUBIA, 11. Sp. 
PLATE XCIII, FIG. 15. 
Shell large, elongate-ovate; length and height as five to three; basal margin 
regularly curving for more than the anterior half of its length, slightly sinuate 
to the posterior extremity, which is narrowly rounded. Anterior end short, 
contracted beneath the beak and rounded below. 
