i 



NO. 5 UPPER CAMBRIAN TRILOBITES RESSER I9 



The cranidium is nearly as wide as long and is well rounded oft at 

 the anterior corners. The second pair of glabellar furrows is fairly 

 distinct although they fail to register in the photograph. In cross 

 section the glabella is moderately high with a somewhat flattened top. 

 Longitudinally its profile is rather straight in the rear, dropping off 

 steeply in the anterior fourth. Brim of average width, slightly thick- 

 ened and situated considerably below the dorsal furrow. Fixigenes 

 very narrow ; about the same width as the brim at the anterior angles, 

 and at their widest point they equal about a fourth the glabellar width. 

 They are rather highly arched so that they partly overhang the eye 

 band. 



Wilberns formation; (loc. 14b) Cold Creek, opposite north end 

 of Sponge Mountain ; (loc. 70) Baldy Mountain, 8 miles northwest of 

 Burnet, Texa^.. 



Holotype.—U.S.NM. No. 108655. 



IRVINGELLA ALTA, new species 

 Plate 3, Figures 16-18 



The wide glabella is only about a fifth longer than wide. The entire 

 cranidium is highly convex in both directions, with the posterolateral 

 limbs depressed almost to a vertical position. The dorsal furrow is 

 narrow. Three pairs of glabellar furrows are visible; both the 

 occipital and the rear pair are relatively narrower and less deep than 

 usual. Laterally the glabella is almost evenly curved, with a tendency 

 toward forming a keel in the middle. The longitudinal profile is 

 circular except in the anterior fourth where the curvature increases 

 until the anterior glabellar lobe overhangs the brim. Brim narrow 

 and compressed closely against the glabella. Fixigenes are less than 

 a third the glabellar width and slope downward at a sharp angle from 

 the dorsal furrow. The eyes are long and somewhat angulated at the 

 widest point of the palpebral lobe. Surface of test evidently smooth. 



Honey Creek limestone ; (loc. 9p) about 15 miles northwest of Fort 

 Sill, Wichita Mountains, Oklahoma. 



Holotypc.—IJ.S.NM. No. 108656. 



IRVINGELLA DECKERI, new species 

 Plate 3, Figures 19-27 



This species is represented by numerous cranidia. Specimens vary 

 considerably in size, but their average is about that for the genus. 



Taken as a whole the cranidium has a more ovate shape than many 

 other species. The large glabella is rounded in front. Dorsal furrow 



