NEW OSTRACODERM— 0RVIG 



which is contained in drill cores from various places in eastern Mon- 

 tana, has proved to be of considerable interest, and together with other 

 undescribed vertebrate material from the Ordovician of Wyoming and 

 South Dakota it will be dealt with by the writer on a future occasion. 



R.82VV 



k^/<'^ GraniFe 



^^^ Dead wood 

 formaHon 



formah'on 



Carboniferous, 

 Permo-Triassic, 

 Jurassic 



Crel-aceous, 

 and yovnaer 



---- faults 



Figure 1. — Map showing the outcrops of Ordovician rocks on the eastern slope of the 

 Bighorn Mountains in the area west of Lake De Smet and Buffalo, Johnson County, 

 Wyo. Redrawn and to some extent simplified from the geological maps of the Bighorn 

 Mountain Region published by Darton (1906a, pi. 47; 1906b, pi. 73). 



The new astraspid, Pyc7iaspis splendens, new genus, new species, 

 described in this paper comes from the Upper Ordovician deposits of 

 the Bighorn Mountains of Wyomhig. The histology of the exoskele- 

 ton in this form will be dealt with more in detail in another connection 

 Orvig, in MS., a). 



