I 



NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 21 



the anterior furrow. In cross section it has a distinctly flattened out- 

 line, although it stands completely above the fixigenes. The brim is 

 of normal width, slightly thickened, and because of the depressed 

 anterior angles, appears to be sinuate when viewed from the front. 

 Fixigenes, nearly half the width of the glabella, are convex and slope 

 downward from the dorsal furrow at an angle less than the lateral 

 slope of the glabella. They are also arched longitudinally and contract 

 in the anterior portion to a small fraction of their average width. In 

 dorsal view the anterior fixigenes appear narrow, owing to the nearly 

 vertical position of their outer portions. 



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

 end of Sponge Mountain, San Saba County, Texas. 



Holotypc.—V.S.NM. No. 108659. 



IRVINGELLA ACCINCTA, new species 



Plate 3, Figures 37-39 



The glabella, clearly defined by a rather deep dorsal furrow, con- 

 tracts rather strongly in the anterior portion to a rounded front. In 

 the exfoliated holotype the occipital and two pairs of glabellar furrows 

 are well developed, but the anterior pair seems to be lacking. In cross 

 section the glabella is distinctly flattened, and longitudinally has most 

 of its convexity in the anterior third. The brim is rather wide and at 

 its ends considerably depressed. The anterior fixigenes first slope 

 downward toward the front, then upward to meet the down-turned 

 ends of the brim. The fixigenes at their widest point are about half 

 the width of the glabella. They are convex laterally, rising con- 

 siderably above the bottom of the dorsal furrow and then sloping 

 down more gently, so that the eye is only slightly below the dorsal 

 furrow. The eye band is prominent because of the deep palpebral 

 furrow and the slight thickening of the band. The posterolateral 

 limbs are also curved into a vertical position. 



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

 end of Sponge Mountain, San Saba County, Texas. 



Holotype.— U.S.N. M. No. 108660. 



IRVINGELLA ABRUPTA, new species 



Plate 3, Figures 40-45 



Like the other species at the locality, /. abrupta is about average 

 size for the genus. It is represented by several cranidia. The glabella 

 is prominent both for its large size and for its convexity, the species 

 deriving its name from the latter feature which serves to distinguish 



