CAMBRIAN FOSSILS. 455 



that they represent the same species. There are no good specimens of the 

 head, But there is one very well preserved pygidium. This and the type 

 specimen are illustrated. 



Formation and locality : Middle Cambrian, Flathead formation, Crow- 

 foot section, Gallatin Range, Yellowstone National Park. 



Agnostus bidens, Meek. 

 PI. LXIII, figs. 4, 4a. 



Agnostus bidens Meek, 1873: Sixth Ann. Rept. U. S. Geol. and Geog. Surv. Terr., for 

 1872, p. 463. Walcott, 1884: Mon. U. S. Geol. Surv., Vol. VIII, p. 26, PI. IX, 

 figs. 13, 13a. 



The specimens representing this species include the head and pygidium 

 only. There is considerable similarity between this species and A. inter- 

 str ictus and A. josephus, the latter from the St. Croix sandstone of Wisconsin. 

 They all belong to the Middle Cambrian fauna, and it will be only after a 

 careful examination with an extended series of specimens that the specific 

 characters are well determined. 



The originals of the type specimens were found on the east side of 

 the Gallatin River, above the town of Gallatin, they being associated with 

 essentially the same fauna as that with which they occur in the Gallatin 

 Range. 



Formation and locality: Middle Cambrian, Flathead formation, Crow- 

 foot section, Gallatin Range, Yellowstone National Park. 



Agnostus tumidosus Hall and Whitfield. 



PI. LXIII, figs. 5, 5a, 



Agnostus tumidosus Hall and Whitfield, 1877; TJ. S. Geol. Expl. 40th Par., Pt. II, 

 p. 231, PI. I, fig. 32. 



This species is represented by a small cephalic shield, and there is an 

 associated pygidium that is referred to it. The species was founded upon a 

 small head discovered in the Eureka district of Nevada. It is a strongly 

 marked species and not liable to be confused with any other species of the 

 genus from the Cambrian rocks of the Rocky Mountain region. 



Formation and locality: Middle Cambrian, Flathead formation, Crow- 

 foot section, Gallatin Range, Yellowstone National Park. 



