NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 37 



turned backward, so that the second and third pairs form a faint cross 

 on the glabella. Laterall}- the glabella is rather evenly but flatly 

 arched ; longitudinally it is considerably curved. The brim continues 

 the rounded curvature of the glabella and consists of a preglabellar 

 area and a narrow, wirelike rim, but faintly indicated. Fixigenes at 

 their widest point are about one-fifth of the glabellar width, and they 

 maintain practically the same width throughout. The eyes are of 

 normal size, situated about the midpoint of the cranidium. A faint 

 tubercle which has more the appearance of a median eye than of a 

 spine occurs on the occipital ring. 



Hamburg limestone; (loc. 23d) near Hamburg j\Iine, Eureka 

 District, Nevada. 



Holotypc.—V.S.XM. No. 108687. 



CHOLOPILUS (?) ALBERTENSIS, new species 

 Plate 10, Figure 3 



This cranidium of doubtful generic position is described in order to 

 present the faunal element. Because there are no good illustrations 

 of the type of Cholopilns extant, one cannot be sure that the published 

 drawings rightly portray the glabellar proportions. The general ap- 

 pearance of this trilobite places it nearest to Cholopilns, in which 

 genus it may be placed for the present. 



The glabella is wide, occupying more than half the cranidial area. 

 It is defined by a dorsal furrow so faint that it disappears in certain 

 light. This cranidium is convex in both directions, the curvature being 

 greater longitudinally than laterally. The anterior margin is slightly 

 indented in the middle and a very faint rim is indicated. 



Lyell formation; (loc. 64b) Glacier Lake Canyon Valley, 48 miles 

 northwest of Lake Louise, Alberta. 



Holotype.—VS.^M. No. T08733. 



CALYPTOMMA, new genus 



A small trilobite characterized by simplicity of structure. The large 

 glabella is quadrate except for constriction at the anterior angles. 

 Glabellar furrows are very faint even on exfoliated specimens. Brim 

 a simple bar. Fixigenes very small, confined to the palpebral lobe, 

 and in the genotype are less than half the width of the eye band. Eyes 

 so large that they envelop the glabella, extend from the forward 

 margin of the glabella beyond the occipital ring. E3'e band wide. 



This genus resembles Cholopilns Raymond in the simplicity and 

 arrangement of the various cranidial parts. It differs from that genus 



