NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 'J'J 



of which a postaxial ridge extends to the indented median margin. 

 The pleural platforms are shaped as small triangles, considerably 

 curved to meet the wide concave border. This border develops sizeable 

 flanges at the posterior angles, giving the rear a rather straight 

 margin and the entire pygidium a quadrate shape. 



Wilberns formation ; (loc. 69) Honey Creek, 8 miles southeast of 

 Llano, Texas. 



Holotype.—\5S.'^.\\. No. 108780. 



PTEROCEPHALINA NOTHA, new species 



Plate 14, Figures 34-38 



The pygidium is typical of the genus. The associated cranidium 

 assigned to the species differs from the head supposed to represent 

 P. bilobata, but is like those assigned to the other species of the genus. 



The glabella which has two pairs of short furrows, tapers to a 

 poorly defined front, as shown in the side views. This characteristic 

 is due not only to the shallowness of the anterior dorsal furrow but 

 also to the fact that the preglabellar area and the anterior fourth of 

 the glabella form a slope of uniform curvature to the depths of the 

 concavity in the brim. The wide brim rises sharply and the outer 

 portion of the rim is somewhat thickened. A slight change in slope 

 marks the inner edge of the rim which in itself is very concave. 

 Since it is so poorly marked, light must strike this angle properly in 

 order to make it visible. It will be noted that the rim is scarcely 

 perceptible in the dorsal view and in one of the side views. The 

 fixigenes rise rather steeply to the palpebral lobes, on which a strongly 

 curved eye occupies a prominent position because it has a wide 

 swollen eye band. Preglabellar area and part of rim marked by 

 vertical anastomosing lines. In the pygidium the axis is long and 

 rather slender, a postaxial ridge connecting it with the indented 

 median margin. A wide border is produced by the concave portion 

 underlain by the doublure. 



Mendha limestone; (loc. 7j) i mile north of Italian Ranch foot- 

 hills, north end of Quinn Canyon Range, Nevada. 



Holotype. — U.S.N.M. No. 108781a; paratypes, Nos. io878ib-d. 



PTEROCEPHALINA BILOBATA (Hall and Whitfield) 



Plate 14, Figures 39-43 



Dikelloccphahis (Pteroccphahis) bilobatus Hall and Whiteield, U. S. Geol. 



Expl. 40th Par. vol. 4, p. 226, pi. 2, fig. 36, 1877. 

 Dicclloccphahis bilobatus Walcott, U. S. Geol. Surv. Monogr. 8, p. 40, 1884. 



6 



