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 Pkillipsia coronata of Walcott (Inc. fit.) 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 ana. 

 and in this feature resembles C. craspedola, 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 tw r o. 



Distribution. Hamilton group. Cyphaspis ornata, and var. baccata occur asso- 

 ciated with Cyphaspis craspedota, Proitus Rowi, Proitus 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 Pha'e- 

 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 Pha, i thon- 

 ides, on account of its characteristic pygidium, it may be probable that the other 



