NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 23 



brim. The eyes are long, extending" almost from the occipital furrow 

 to a point beyond the anterior angle of the dorsal furrow. They first 

 curve outward from their rear end for about a third of their length, 

 then bend at a rather sharp angle tow^ard the glabella. 



Wilberns formation; (loc. 70) Baldy Mountain, 8 miles northwest 

 of Burnet; and (loc. 14b) Cold Creek, opposite north end of Sponge 

 Mountain, San Saba County, Texas. 



Holotype. — U.S.N.M. No. 108662a; paratypes, Nos. 108662b, 

 108663. 



IRVINGELLA ALBERTA, new species 

 Plate 4, Figures 1-3 



The wide glabella tapers more rapidly than the average for the 

 genus. The occipital and first pair of glabellar furrows are very deep 

 and wide. The middle pair consists of short, sharply impressed inden- 

 tations at the sides of the glabella, and the anterior pair appears only 

 as slight depressions. Laterally the glabella stands completely above 

 the dorsal furrow, its outline being slightly flattened on top. Longi- 

 tudinally it is curved throughout. The brim is evenly convex and of 

 average width. The fixigenes are less than one-third the glal)ellar 

 width anterior to the eyes, narrowing rapidly to match the rim width. 

 Owing to the sharp depression of the anterior angles and the tapered 

 glabella the entire cranidium narrows perceptibly forward. 



Lyell formation ; (loc. iQu) Johnson Creek, 8 miles east of Lake 

 Louise, Alberta. 



//0/0/y/^r.— I'.S.N.M. No. 108664. 



IRVINGELLA RICHMONDENSIS, new species 

 Plate 4, Figures 4-6 



This small species with a wide cranidium has relatively the widest 

 fixigenes of any Nevada species. 



The glabella is subcylindrical, tapering slowly forward. The occi- 

 pital and first pair of glabellar furrows are narrow and their position 

 is more nearly parallel to the rear margin of the glabella than is 

 usually the case. Laterally the glabella has a nearly semicircular 

 outline. Longitudinally it is rather convex, increasing in convexity 

 from the rear margin forward. The brim is relatively large and some- 

 what thickened, sloping down in line with the declivity of the head. 

 Fixigenes more than half the width of the glabella, decreasing in their 

 anterior portions to the width of the brim. Longitudinally they are 



