NO. 5 UPPER CAMBRIAN TRILOBITES^RESSER 8l 



ring. The preglabellar area is less than one-fourth the rim width. 

 Longitudinally the convexity of the cranidium is so great that the 

 front fourth has taken the position of a 90° angle with the posterior 

 portion of the glabella. From that position the brim takes a less steep 

 angle and is in itself nearly flat. In cross section the glabella is also 

 very convex, attaining a height equal to about one-third its length. 

 Because the anterior angles are also greatly depressed this species 

 becomes one of the most convex Cambrian trilobites. 



The associated libragene is large. The wide and long ocular plat- 

 form is only slightly convex and lacks a furrow. Toward the long 

 genal spine the libragene becomes convex forming a ridge that extends 

 into the genal spine. Elevated portions of surface of head and cheek 

 coarsely granulated. 



Davis formation; (loc. iik) Federal Lead Mine No. 4, Flat River, 

 Missouri. 



Holotypc. — U.S.N.M. No. 108801a; paratype. No. 108801b. 



BURNETIA EXTENSA, new species 

 Plate 17, Figures 15-22 



This species is abundantly represented by numerous cranidia, several 

 libragenes, and possibly also by a pygidium. It is the extreme of the 

 linguloid forms thus far found. It will be observed that a slight 

 variation has been allowed among the specimens figured. 



The glabella, rounded in front, has two pairs of furrows. The 

 occipital furrow is almost interrupted at the center, and the neck ring 

 carries a large spine. The brim, which comes to a rather sharp point, 

 exceeds the length of the glabella exclusive of the neck ring. A 

 narrow preglabellar area is present. Eyes are strongly bowed and have 

 heavy eye bands. The libragenes illustrated show that the suture is 

 intramarginal for a considerable distance and that the wide doublure 

 apparently extends all the way across, with an increase in width 

 toward the middle. The associated pygidium has a long, stout axis 

 and pleural lobes that are slightly convex, sloping to a concave border. 



Honey Creek limestone ; (loc. 89V) West Timbered Hills, Arbuckle 

 Mountains, Oklahoma. 



Holotype. — U.S.N.M. No. 108807a ; paratypes, Nos. io88o7b-g. 



BURNETIA EXILIS, new species 

 Plate 17, Figures 23-27 



This species also is well represented by cranidia. Because of its 

 nearly circular anterior outline it is closer to the normal form. In 



