CRUSTACEA. 
147 
right free cheek shows the genal angle produced into a broad sub-acute spine; 
the lateral margin carries a row of tubercles which continue with diminishing 
size to the angle of the cheek; the lateral sub-orbital area bears a few strong 
tubercles, the interspaces of the surface being faintly pitted. 
The PhilUpsia coromta of Walcott (loc. cit.) is a somewhat distorted fragment 
of a cephalon from Newark Mountain, Eureka District, Nevada. The original 
specimen differs from the type of Cyphaspis ornata in its convex frontal area, 
and in this feature resembles C. craspedota, of the Hamilton group, but the 
ornamentation of the frontal and lateral areas and of the border is similar to 
that of the former species, and the specimen thus appears to represent a form 
intermediate between the two. 
Distribution. Hamilton group. Cyphaspis ornata, and var. baccata occur asso¬ 
ciated with Cyphaspis craspedota, ProHus Rowi, Proetus macrocephalus, Phacops 
rana, and Dalmanites Boothi, var. Calliteles, in the limestones at the base of the 
Hamilton shales, near Centerfield, Ontario county. C. ornata is also known 
from the upper shales at Fall Brook, Hopewell, and Canandaigua Lake, Ontario 
county, and Eighteen-mile Creek, Erie county. 
Our knowledge of the species Cyphaspis ornata, Cyphaspis hybrida, and Phae- 
thonides varicella, is yet so imperfect that the details of structure here given 
may eventually prove only of varietal value. The points of difference upon 
which the species are now separated are as follows; C. ornata is usually very 
sharply pustulose and minutely punctate on the frontal area, a single example 
which retains the characteristic beaded border, being strongly pitted and 
affording a transitional form to the species C. hybrida, which is strongly 
punctate upon its entire surface bearing an elevated border upon which the 
tubercles are obsolescent. In Ph. varicella the surface is both tubercled and 
punctate, but not so strongly tubercled as in C. ornata, nor so strongly punctate 
as in C. hybrida, while the margin is thin and without tuberculations. 
As it has been necessary to refer one of these species to the genus Phaethon- 
ides, on account of its characteristic pygidium, it may be probable that the other 
