4 
220 THE AMERICAN MIDLAND NATURALIST. 
being irregularly conical, and others rounded, with sharp points 
fringing the distal ends, and are without definite pattern on 
the outer portion, with an excentric elevated central portion, 
generally roughly polygonal, which bears in the center an 
elevated boss for the attachment of the spine, and near the 
periphery a series of small knobs or granulae. 
Remarks.—This genus is based on a single species, N. pri- 
mus, of which remains are common in the Hackberry stage. 
It is distinguished by the shape of the plates and their orna- 
mentation, and the distally enlarged spines. 
NORTONECHINUS PRIMUS n. sp. 
Plate, Figs. 1-8. 
Description.—This species has been fully described in the 
genus diagnosis. The commonest spines are the broad, flattened 
ones, which evidently covered the general surface of the body. 
Other types are the elongate-polygonal ones, and the heavy, 
club-shaped forms, which are marked by fine vertical lining, 
and in the latter case, are without granulose ornamentation 
on the distal surfaces. These two types of spine are uncommon, 
but may be found associated with the flattened ones. The 
third type is that shown in Fig. 6: an elongate spine, heavier 
at the proximal end than at the cistal. The length of one of 
these, which is incomplete, is 16 mm.; diameter at base 2.7 
mm.; diameter about midway of the length 2.8 mm. Probably 
these spines correspond in position to the long, flattened ones 
of Colobocentrotus. 
Remarks.—The writers are particularly indebted to Dr. 
Stuart Weller for assistance in working out this, the most 
characteristic of the Hackberry echinoderms. 
Distribution.—Throughout the Spirifer zone of the Hack- 
berry, near the base of that division. 
