NO. 3 CAMBRIAN TRILOBITES , 213 



elongate glabella of the Alabama specimens is similar to that of the 

 variety elongatiis of Wisconsin. 



The identification of the species at the two localities is strength- 

 ened by the occurrence in both areas of similar variations in the 

 form of the glabella, frontal limb, furrow, and border of the 

 cranidium. 



The stratigraphic position of the Texas and Alabama specimens 

 is the same to the extent that both occur in the lower part of the 

 Upper Cambrian. 



In the Cordilleran region an apparently identical cranidium and 

 pygidium occur in the Upper Cambrian (358c) Abrigo limestone of 

 the Bisbee mining district, Cochise County, Arizona. The cranidia 

 are typical forms with intermediate and broad frontal border. An 

 apparently identical cranidium and pygidium occur in the (i5ig) 

 Gallatin limestone of northern Wyoming (fig. 4, pi. 30). The 

 cranidium has the wide glabella, variable frontal border, and coarsely 

 granular surface of C. texanus (compare fig. 4 with figs. 2 and 2h, 

 pi. 30). A somewhat similar form with a wide flattened frontal 

 border occurs in the Gallatin limestone of Meagher County, Mon- 

 tana, that is identified with the variety elongatiis of the Eau Claire 

 formation of Wisconsin (pi. 29, fig. 4). 



The critical study of this species with new material results in 

 removing the form described by Whitfield as Arionellus tripunctatus 

 from C. texanus, to which I referred it in 1899,* ^^^^ referring it to 

 Crepicephalus as a distinct species characterized by an occipital 

 spine and narrower glabella. 



Formation and locality. — Upper Cambrian: (67a) Cap Mountain 

 formation (upper beds) ; limestone on Potatotop Hill, 6 miles (9.6 

 km.) northwest of Burnet; also (i4d) Bartlett Hollow, 2 miles 

 (3.2 km.) southeast of mouth of Fall Creek, 17 miles (27.2 km.) 

 northwest of Burnet, both in Burnet County, Texas. 



Upper Cambrian: (358c) Abrigo limestone; north side Moore 

 Canyon, west edge Bisbee quadrangle, Bisbee district, Arizona. 



Upper Cambrian: (151b) Gallatin limestone; below saddle on 

 ridge between Pebble Creek and Soda Butte Creek, Yellowstone 

 National Park, Wyoming. 



Upper Cambrian: (i5ii) Gallatin limestone; 6 miles (9.6 km.) 

 northeast of White Sulphur Springs, Meagher County, Montana. 



Upper Cambrian: (90a and 91) Conasauga formation; Cedar 

 Bluff on Coosa River, Cherokee County, Alabama. Entire speci- 



Monogr. No. 32, U. S. Geol. Survey, p. 460. 



