NO. 3 CAMBRIAN AND OZARKIAN TRILOBITES I23 



Formation and locality. — Middle Cambrian: (62f) Chetang for- 

 mation. Shaly bed in bluish gray limestones ; Southwest base of 

 Robson Peak about 600 feet (182.9 m.) from base and 300 feet 

 (91.4 m.) above Lake Kinney, Robson Park, British Columbia, 

 Canada. 



Genus WILBERNIA Walcott 



Wilbernia Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. 2, p. 60. 



The glabella is about three-fourths as long as the cranidium and 

 rectangular in outline, rounded in front. Two pairs of glabellar 

 furrows are usually visible on the inner surface of the test, but are 

 faint or absent on the outer surface. The occipital ring is fairly wide, 

 and the furrow is usually strongly defined. 



Fixed cheeks about one-third as wide as the glabella in advance of 

 the eyes. Ocular ridges present or indicated on most specimens. 

 Eyes moderately large, and the mid point is back of the middle of 

 the glabella. The palpebral lobes have a tendency tO; rise above the 

 fixed cheeks, and in some species they are raised into a boss-like 

 protuberance. 



The facial suture diverges considerably in front of the eyes and 

 is intramarginal for some distance. The postero-lateral limbs are 

 long and narrow. 



Cranidium with a wide frontal limb, in which the border and rim 

 occupy relatively varying portions of the whole. The rim is always 

 wide and well defined by a shallow furrow. 



Free cheeks with long genal spines and a rim as wide as that of the 

 cranidium. A doublure of equal width extends all the way across 

 beneath the head. No epistoma nor median suture has been seen. 



The pygidia of the species of this genus have a high, very convex 

 axis, and approximately flat sides. The axial rings clearly marked 

 by deep furrows. The axis extends back more than three-fourths 

 the length of the tail, and often widens out with a tendency toward 

 the formation of small nodes at the end. A descending, narrow ridge 

 connects the posterior end of the axis proper with a flattened border. 

 Its width increases toward the anterior margins. Four or more 

 lateral pleurae are visible in the tail. They are closely fused but have 

 the dividing furrows well marked. The pleural furrows are wide and 

 clearly impressed. 



Derivation of name. — Wilberns formation. 



Genotype. — Ptychoparia pero Walcott. 



Range. — Upper Cambrian : Mississippi Valley and Rocky Moun- 

 tains. 



