NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 45 



The libragenes have short slender genal spines. 

 Maurice formation ; (loc. 26c) T. 30 N., R. 96 W., 6 miles south of 

 Hailey, W3'oming. 



Holotype. — U.S.N.M. No. 108700a; paratypes, Nos. 108700b, c. 



ARAPAHOIA POLITA, new species 

 Plate 7, Figures 10, 11 



The cranidium, exclusive of the large occipital spine and postero- 

 lateral limbs, forms approximately a rectangle. A weakly defined 

 dorsal furrow showing on the upper surface, probably is strongly 

 indicated in exfoliated specimens. In cross section the cranidium is 

 flatly arched but longitudinally the front third turns down rapidly. 

 The eyes are of moderate size, situated at about the midpoint of the 

 cranidium. Facial suture diverges sHghtly in front of the eye and 

 rapidly behind the eye to form large posterolateral limbs. A broad, 

 shallow furrow separates the greatly thickened neck ring which ex- 

 tends into a long, tapering, up-curved spine, the sides of which are 

 strongly striated. No other parts have been assigned to the species. 



Sullivan formation; (loc. 6411) East Lyell Glacier, 48 miles north- 

 west of Lake Louise, Alberta. 



Holotype— V.S.N. M. No. 108701. 



ARAPAHOIA ELONGATA, new species 



Plate 7, Figures 15-19, 32 



This is a common species of the group found in this abundant 

 fauna. It is characterized by a relatively narrow, long, tapering 

 glabella which in exfoliated specimens is outlined by a shallow dorsal 

 furrow. Fixigenes narrow. Eyes small. Facial suture diverges in 

 front of eyes, then becomes intermarginal for a considerable distance, 

 rounding the anterior angles. In cross section the head is flat, and 

 longitudinally it has about the same flat curvature, except at the front 

 edge, where it is rolled under slightly. The neck spine evidently was 

 long. The libragene assigned to this species is rounded in contour on 

 all edges, and in exfoliated specimens shows faint lines radiating from 

 the eye. The pygidium assigned to the species is smooth and evidently 

 has a punctate surface, but lacks a well-differentiated border. 



Sullivan formation; (loc. 64h) East Lyell Glacier, 48 miles north- 

 west of Lake Louise, Alberta. 



Holotype. — U.S.N.M. No. 108703a; paratypes, Nos. 108703b, c.' 

 4 



