ORDOVICIAN FAUNAS. 211 
above and in front of the central pit. A slight, moderately-sharp, 
oblique ridge extends from the dorsal margin, near the anterior ex- 
tremity of the hinge-line, forward and downward to above the middle 
of the anterior extremity of the body of the shell. Free margin 
bordered throughout by a rather broad, concave frill. Surface very 
finely punctate, the marginal frill marked by more or less obscure, 
radiating lines. 
The dimensions of an average specimen are: length, 2.3 mm.; 
height, 1.5 mm.; length of hinge-line, 1.7 mm. 
Remarks—This species closely resembles the last one in many of 
its characteristics, but may always be distinguished from it by reason 
of the absence of the convex marginal area within the marginal frill 
and by its much wider frill. 
DESCRIPTION OF SPECIES FROM THE Hupson RiIvEeR FORMATION. 
The slates and arenaceous beds of the Hudson River formation are 
almost barren of organic remains, and at only three localities have 
fossils been found. At Sussex there is a thin stratum containing 
many individuals of but very few species of brachiopods. The other 
two localities, one near Branchville and the other in the railroad cut 
at Jutland, have afforded only graptolites. 
COELENTERATA. 
HYDROZOA. 
DIPLOGRAPTUS FOLIACEUS (Murch.). 
Plate XVI., Fig. 7. 
184%. Graptolithus pristis Hall, Pal. N. Y., vol. L., p. 265, pl. 72, 
figs. 1 a-s. 
Description.—Polypary flat, straight, celluliferous on two sides, be- 
coming gradually broader from the distal extremity for one-half to 
two-thirds of their length, and then again becoming a little narrower. 
The maximum width attained is from 2 mm. to 2.5 mm. About four- 
