NO. 5 UPPER CAMBRIAN TRILOBITES RESSER 75 



outward curvature of the dorsal furrow slightly anterior of the mid- 

 point of the eye, which creates a small side lobe on the glabella. The 

 concave brim is a little more than one-third the glabellar length. A 

 sudden increase of curvature develops a broad, shallow anterior 

 furrow near the middle of the brim. Between the eyes, with their 

 broad bands, the fixigenes are confined to the palpebral lobes, which 

 are not as wide as the eye band. Anterior to the eye the facial suture 

 diverges rapidly, developing large anterior angles. Since the eyes 

 extend almost to the occipital fiuTow, there is almost no fixigene 

 behind the eye, and the posterolateral limbs are therefore very narrow. 



The pygidium has the typical oval shape, with a tapering axis that 

 occupies about two-thirds its length. A light postaxial ridge is 

 traceable to the margin. Longitudinally the axis is slightly convex, 

 dropping to the nearly flat border with a smooth concave curve. 

 Furrows, weak on the axis, become clearly defined on the pleural lobes 

 when the test is exfoliated. 



Pilgrim formation; (loc. 20y) 3 miles north of Trident, north of 

 Logan, Montana. 



Holotype. — U.S.N.M. No. 108786a ; paratypes, Nos. io8786b-g. 



COOSELLA Lochman, 1936 

 COOSELLA TEXANA, new species 



Plate 13, Figures 21-24; Plate 14, Figures 2-5 



The first species of Coosclla, typical in all respects, to be recog- 

 nized in Texas occurs at two localities. Only the holotype cranidium 

 and the nearly complete pygidium were collected at one locality, but 

 several of each of the parts occur at the other place. 



The large glabella tapers rapidly to the rounded front. Faint broad 

 depressions shadow the glabellar furrows. The brim wddth equals a 

 little less than one-third the glabellar length. Li cross light the brim 

 is simple and concave, but when the lighting is from the front a broad, 

 slightly thickened rim is demarcated b}^ a shallow anterior furrow. 

 The diagonal set of the eyes and the nondivergence of the anterior 

 facial suture cause the brim to be much shorter than the rear of the 

 cranidium, producing the pinched eftect in the anterior part of the 

 cranidium characteristic of the genus. At the anterior end of the eye 

 lobe the fixigene equals half the glabellar width at the same point, 

 while at the rear of the eye lobe the same relationship is less than 

 one-third. This shows that the fixigene retains its width but little 

 changed, whereas the glabella expands rapidly. The eyes are of 

 normal size, situated opposite the anterior portion of the glabella, and 

 are set parallel to the dorsal furrow. 



