20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, IO3 



shallow but clearly defined. Occipital furrow narrow. First pair of 

 glabellar furrows continues across center unchanged in width but the 

 anterior pairs are not visible. Laterally the glabella is moderately 

 convex, with concentration of the greatest convexity near the center. 

 Longitudinally the rear half is only slightly convex, but in the anterior 

 portion the convexity increases until the slope becomes vertical. The 

 brim is narrow and slightly thickened, sloping down from the anterior 

 furrow. Fixigenes are about one-third the width of the glabella, their 

 anterior portion measuring about one-third their average width. The 

 eyes are as long as the glabella, extending beyond the line of the 

 lateral dorsal furrow in front. The fixigenes slope downward rather 

 evenly from the dorsal furrow. 



Honey Creek limestone; (loc. SQy) West Timl)ered Hills, Arbuckle 

 Mountains, Oklahoma. 



Holotype. — U.S.N.M. No. 108657a; paratypes, Nos. 108657b, c. 



IRVINGELLA BURNETENSIS, new species 



Plate 3, Figures 28-33 



The cranidia representing this species are of average size and, as 

 the illustrations show, are rather typical in form. The cranidium is 

 subcylindrical in shape. The dorsal furrow is wide and relatively deep, 

 as are the other furrows. The glabella, convex in both directions, 

 stands completely above the libragenes. Li cross section it has a sub- 

 circular outline and longitudinally it is curved throughout, but has 

 nearly all of its convexity in the anterior half. The brim is relatively 

 wide and flat, with rather sharply depressed ends. The fixigenes are 

 about one-third the width of the glabella and their anterior portions 

 are about half of their average width. The eyes are long, extending 

 forward almost the full length of the glabella. 



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

 of Burnet, Texas. 



Holotype— U.S.^M. No. 108658a; paratypes, Nos. 108658b. c. 



IRVINGELLA BACCA, new species 

 Plate 3, Figures 34-36 



This small, well-defined species is not as abundantly represented as 

 the others found at the locality. The glabella contracts slightly to a 

 rounded front. Occipital and rear glabellar furrows deeply impressed ; 

 anterior pair faint and the median pair well developed as shown in 

 side view. The entire cranidium is convex longitudinally, the glabella 

 having its greatest convexity in the anterior half, where it overhangs 



