316 CARBONIFEROUS FORMATIONS AND FAUNAS OF OOI>ORAUO. 



(//.sv'.v is sinootli. 'Plu' cophala rot'erred I)}' Hall and Whitfield to /'. perof.mdi'.iix, 

 however, while eorresp()ndin<>-ly larger than the pygidiuiii upon which /'. loganeTViw 

 is based, and tlunit^li oc-ciirrin<i' oti the same slab as the types of /'. jii'voccidensi, are 

 yet entirely witliout the ornamentation of the latter species. 



During the past few years I have handled more or h-ss material containing this 

 fauna, and in it have noticed on several occasions a large cephalic shield ornamented 

 with numerous prominent nodes. At station 2382. in the San Juan region, one 

 of these ornamented cephala is associated with an ornamented pygidiuni clearly 

 belonging to the species P. peroccldens, while in Yellowstone Park the smooth heads 

 and pygidia occur together. It seems quite conclusive, therefore, that part of 

 P. jperoceidens as defined by Hall and Whitfield, and all of that species as defined 

 by myself, must go with P. loganensw. These changes in synonymy have been 

 made in the list preceding this discussion. 



This species, in view of the large number of segments in the axis of the pygi- 

 dium, the distinctness of the lateral lobes of the glabella, and the strong circular 

 basal lobes, should, it seems, be pi-operly referred to the genus Ph/illijma. 



Locality and harizon. — San Juan region (station 2382); Ouray limestone. 



LEPERDITIA Rouault. 1851. 

 Leperditia sp. 



Two specimens of ostracodes, one a Lepei^ditia, the other a Beyrichia, were 

 found in the Millsap limestone at Perr}- Park (station 2389). The material is both 

 scanty and imperfect, but since these were the only ostracodes obtained from this 

 horizon it has seemed worth while to make some record of their presence. 



The single Leperditia is preserved as an internal cast. It is a small left valve 

 having a width of about 2 mm. and a height of li mm. The convexitj' is moderate. 

 The anterior end is somewhat narrower than the posterior. The posterior outline 

 appears to have little or nothing of a backward swing, but is rather regular h" 

 rounded, meeting the ventral outline possibly somewhat abruptly. There are indica- 

 tions of a large, round, subcentral, muscular imprint, but I am not sure that what 

 appears to be such is not an accidental character of the rock. The ocular tubercle I 

 have been unable to distinguish. 



Locality and Juyrizon. — Castle Rock quadrangle (station 2389); Millsap limestone. 



BEYRICHIA McCoy, 1844. 



Beyrichia sp. 



Like the preceding, this species, of which a single specimen has been found, is 

 represented as an internal cast in white chert, in which the fossils of this horizon 

 chiefly are found. The shell, which is a right valve, is quite a small one, having a 



