22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



it from its associates. In the exfoliated holotype the occipital and the 

 three glabellar furrows increase in depth toward the rear of the 

 cranidium. The dorsal furrow is broad and on the outside of the test 

 is indicated only by change of curvature. The glabella is constricted 

 anteriorly by the circular course of the dorsal furrow. Laterally the 

 glabella is highly arched, being only slightly flattened on top. Longi- 

 tudinally it is very convex so that the front half slopes downward 

 sharply from the horizontal line. The thick brim is sinuate in front 

 view and is slightly up-turned with respect to the anterior furrow. 

 Fixigenes nearly half the width of the glabella, narrowing rapidly 

 forward from their midpoint, to one- fourth average width. Eyes 

 moderately long extending from about the ends of the occipital furrow 

 forward to the anterior angles of the dorsal furrow. In dorsal view 

 the eyes curve only slightly for half their length from the occipital 

 furrow, then more abruptly. Laterally the fixigenes are only slightly 

 convex, except where they are rolled under at their outer edges, and 

 as a whole assume a nearly horizontal position with respect to the base 

 of the cranidium. Longitudinally they conform to the great convexity 

 of the head, but more by means of sloping forward as a whole than 

 by curving. In this respect /. ahrupta is unique. Test smooth, but 

 exfoliated specimens have the usual strongly punctate surface. 



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

 end of Sponge Mountain, San Saba County, Texas. 



Holotype.— IhS.'HM. No. 108661a; paratype, No. 108661b. 



IRVINGELLA MEDIA, new species 



Plate 3, FicuitEs 46-54 



This relatively small, aljundant species is wider than the other 

 Texas species and in this respect finds closer relatives in the Canadian 

 Rockies. 



The glabella is long, narrow, and considerably constricted toward 

 the front. The occipital furrow and rear glabellar furrows are wide 

 and fairly deep, while the anterior pairs have normal dexelopment. 

 Viewed vertically, this species seems to be very broad and flat. From 

 the front it is broad even though the glabella is highly arched. Longi- 

 tudinally, however, as the side views show, this species is strongly 

 convex. The brim is rather wide and has a somewhat thickened edge 

 and a shallow anterior furrow. The fixigenes at their widest are 

 about half the width of the glabella at the same point. Their rear 

 moiety is nearly rectangular in shape, but the anterior jiortion de- 

 creases rapidly in width, being reduced finally to the width of the 



