XO. 5 UPPER CAMBRIAN TRILOBITES — RESSER I 5 



the shortest of any species observed. The anterior fixigenes are 

 sHghtly abnormal owing to the presence of a shallow anterior furrow, 

 which causes them to appear tumid in lateral section. Laterally the 

 fixigenes are only slightly convex, except at their outer edges, and 

 as a whole slope downward from the dorsal furrow. The eye band 

 is upturned a little. 



Honey Creek limestone ; (loc. 89W) west side of the West Timbered 

 Hills, Arbuckle Mountains, Oklahoma. 



Holotype. — U.S.N.M. No. 108646a; paratypes, Nos. 108646b, c. 



IRVINGELLA MESLERI, new species 



Plate 2, Figures 34-38 



This average-size species is represented by a number of cranidia. 



The long glabella decreases in width forward to the rounded anterior 

 outline. Occipital and first pair of glabellar furrows deep ; two other 

 pairs visible. The dorsal furrow is wide and moderately impressed. 

 The brim is rather wide and thick in the middle, and has a rimlike 

 edge owing to the presence of an incipient anterior furrow. Fixigenes, 

 at their widest point, nearly half the glabellar width. Their anterior 

 portions, which are short owing to the fact that their greatest width 

 occurs far forward, are about as wide as the rim and equally convex. 

 The long eyes extend approximately from the occipital furrow to the 

 brim. Laterally the fixigenes are only moderately convex and slope 

 down slightly from the dorsal furrow. 



Honey Creek limestone; (loc. I2n) 7 miles north of Springer, 

 Arbuckle Mountains, Oklahoma. 



Holotype. — U.S.N.M. No. 108647a : paratype. No. 108647b. 



IRVINGELLA RECURVA, new species 



Plate 2, Figures 39-41 



The glabella is rather wide and well rounded in front. The glabellar 

 furrows are broad and deep, and the dorsal furrow is particularly 

 wide and, in exfoliated specimens, also deep. In cross section the 

 glabella stands completely above the dorsal furrow, and is flattened 

 slightly on top. Longitudinally the rear third has a nearly straight 

 profile, while the anterior portion bends down sharply to overhang 

 the anterior dorsal furrow. The narrow brim is slightly thickened, 

 and when viewed from the front has a sinuate outline. The fixigenes, 

 which stand vertical, are only about one-fourth the width of the 

 glabella. They are slightly convex and have considerable width in 

 their anterior portions. 



