NO. 3 CAMBRIAN AND OZARKIAN TRILOBITES I25 



Genotype. — Megalaspis belenimirus White/ 



Range. — Ozarkian and possibly Canadian. Western Cordillera. 



The narrow border on the cranidium places this group nearer the 

 Asaphidae than to the family including Megalaspis. None of the 

 pygidia assigned to Xenostegiuin possesses the pleural furrows charac- 

 teristic of the species belonging to Megalaspis. 



XENOSTEGIUM ALBERTENSIS, new species 



Plate 24, figs. 10, II 



Observations. — Only a pygidium of this form has been thus far 

 found in the collections. It differs from X. goniocercum in its greater 

 general convexity and the strongly convex axis. No trace of axial 

 or pleural furrows. 



Formation and locality. — Ozarkian: (66v) Mons formation. Upper 

 Johnson Creek Canyon, Sawback Range, Alberta, Canada. . 



XENOSTEGIUM BELEMNURUM (White) 



Plate 24, figs. 3, 4 



Megalaspis bclcmnurus White, 1877 (Rept. 1874, P- n), Rept. U. S. Geol. 



Surv., West looth Merid., War Dept., Vol. 4, p. 59, pi. 3, fig. 9. Miller, 



1889, N. A. Geol. Pal., p. 556, fig. 1030. 

 Xenostegium goniocercum (Meek) Walcott, 1924, Smithsonian Misc. Coll., 



Vol. 75, No. 2, p. 60, pi. 13, fig. 5. 



Observations. — A cranidium was discovered in the matrix lying 

 quite close to the pygidium, which is the hologenotype. It is assumed 

 that this cranidium belongs to the same animal as the pygidium 

 (fig. 4) since it agrees quite closely with others at distant localities 

 associated with pygidia congeneric with this one. 



Formation and locality. — Canadian ? (671) Queen Spring Hill, 

 just south of Schellbourne Pass, Nevada. 



XENOSTEGIUM DOUGLASENSIS, new species 

 Plate 24, figs. 22, 23 



Observations. — This species resembles the genotype more closely 

 than any other in the collections. The cranidium is a little more 



^For several years Megalaspis belemnurus White and Asaphus (M.) gonio- 

 cercus Meek were labeled as one species, in the collections of the National 

 Museum, and the genus was published last year before completing the critical 

 study, hence the older established name was chosen as the genotype, but the 

 drawing was based on the proper specimen. 



