292 PALEOZOIC PALEONTOLOGY. 
RHOMBOPTERIA CLATHRATUS Var. 
Plate XXXI., Fig. 15. 
In the Coeymans limestone near Peter’s Valley a single specimen 
of Rhombopteria has been observed, which may represent a species 
distinct from the shell just described. The single imperfect specimen 
is not sufficient, however, to determine this with certainty, and it may 
for the present be considered as a variation of FR. clathratus. Its 
contour is more irregular than that of the typical form of the species, 
the beak is more anterior and, the anterior auriculation is more pro- 
nounced. The surface is, for the most part, exfoliated, but enough 
is retained to determine that its markings are essentially identical 
with FR. clathratus. 
ACTINOPTERIA COMMUNIS (Hall). 
Plate XXXI., Fig. 21. 
1859. Avicula communis Hall, Pal. N. Y., vol. III., p. 286, pl. 52, 
figs. 1-7, pl. 53, figs, 1, 4, 6. 
Description.—‘Shell obliquely ovate; the left valve gently convex in 
the middle, and becoming gibbous towards the beak, which, in the 
young shell, is narrow and projecting above the hinge-line; right 
valve flat or gently concave in the middle and below, and becoming 
slightly convex on the umbo; anterior side gently curving to the base, 
which is broadly rounded, the curvature of the posterior side being 
more abrupt; anterior wing small, trigonal, obtuse at its extremity, 
strongly defined from the body of the shell; posterior wing three 
times as long as the anterior wing, obtusely or subacutely pointed, 
extending more or less beyond the margin of the shell, concave on 
the outer or lateral margin, its junction with the body of the shell 
not strongly defined. 
“Surface of left valve marked by slender, sharply-defined, 
rounded radii, the principal of which are distant from two to four 
or five times their width, and the spaces occupied by one, two or three 
finer interstitial, radiating striw (these radii are but faintly, and some- 
