NO. 5 CAMBRIAN TRILOBITES — RESSER 43 



Plagiura cercops (Walcott) 

 Ptychoparia ? cercops Walcott, Smithsonian Misc. Coll., vol. 67, no. 3, p. 81, 

 pi. 12, figs, i-id, 1917. 



Lower Cambrian, Mount Whyte ; (loc. 63c) i^ miles northeast of 

 Lake Louise, Alberta. 



Cotypes.—V.S.^M. nos. 64377-64381. 



POLIELLA Walcott, 1916 



Poliella Walcott, Smithsonian Misc. Coll., vol. 64, no. 5, p. 349, 1916. 



This genus was established as a subgenus of Bathyiiriscus, with the 

 statement that the pygidium was different. Even a cursory revision 

 of the trilobites referred to Bathyiiriscus and related genera shows the 

 necessity of making this a full genus. Evidently, Walcott first in- 

 tended to use the form from Pole Creek, Bathyuriscus pozuersi, as 

 the genotype, but since he designated the Spence shale form, it be- 

 comes the genotype, and the genus is not represented at the Pole 

 Creek locality. 



Diagnosis. — Cephalon much larger than pygidium. Glabella quad- 

 rate, expanded anteriorly ; two pairs of glabellar furrows usually 

 clearly defined, others very faint or absent. Eyes long, moderately 

 bowed. Brim when present narrow and simple. 



Thorax with 7 to 9 segments. 



Pygidium with wide, well-defined axis ; pleura usually fused ; two 

 to four pleural furrows extend to the margin ; rim absent. 



Comparisons. — Compared with Bathyiiriscus, Poliella is distin- 

 guished by its fewer thoracic segments, larger eyes, and much smaller 

 tail. 



Genotype. — -Bathyuriscus (Poliella) anteros Walcott. 



Range. — Middle Cambrian. 



Species formerly referred to Poliella: 



P. powcrsi:^ Bathyuriscus P. sylla =^ Clavaspiddla 



P. probus = Clavaspidella 



DESCRIBED SPECIES REFERRED TO POLIELLA 



Besides the species discussed below, the following belong to the 

 genus. 



Poliella anteros Walcott Poliella chilo Walcott 



Poliella baliis Walcott 



