NO. 5 CAMBRIAN TRILOBITES 429 



DoUchomctopus productus (Hall and Whitfield) — Continued. page 



3&. (X2.) Hypostoma. U. S. National Museum, Catalogue No. 

 IS4S5C. 

 The specimens represented by figs. 3, 2>a-b are from locality 

 31, Middle Cambrian: Chisholm shale, Ely Mountains, Nevada. 

 The two figures were first published in 1886 (Bull. U. S. Geol. Surv., 

 No. 30, pi. 30, figs. If, id). 



4- (X3-) Small dorsal shield. U. S. National Museum, Cata- 

 logue No. 62713. 



4a. (X2.) Medium sized dorsal shield. By error the front of the 

 glabella was shaded in so as to make it too wide. It has 

 about the same outline as the glabella of figure 4. U. S. 

 National Museum, Catalogue No. 62714. 



The specimens represented by figs. 4, 4a occur in a fine arena- 

 ceous shale at locality 746, Middle Cambrian: Bright Angel shale; 

 Grand Canyon, Arizona. 



DoUchomctopus ? c.vpausus (Walcott ) 36S 



Figs. 5, 5a. (X 2.) Dorsal view and side outline of a cranidium which 

 is the type and only specimen of the species. U. S. National 

 Museum, Catalogue No. 15450. 



The specimen was illustrated on plate 9, fig. 19, by Walcott 

 (Monogr. U. S. Geol. Surv., Vol. 8, 1884). 



The specimen came from locality 55b, Middle Cambrian: El- 

 dorado limestone : Secret Canyon, Eureka District, Nevada. 



