NEW OSTRACODERM— 0RVIG IQ 



what has been said in this paper, one may now distinguish two differ- 

 ent vertebrate faunas in the Ordovician of the Cordilleran Region, 

 one in the Harding Sandstone of Colorado and another in the Pyc- 

 7ia.9pis-bearing beds of the Bighorn Mountains of Wyoming. In 

 addition, there is probably also a third vertebrate fauna — intermedi- 

 arj'', to some extent at least, between the other two — in the material 

 at my disposal from the Winnipeg formation of the Williston Basin 

 in Montana. The latter material has not yet been investigated in 

 detail, but a preliminary examination has shown that it includes 

 plates and scales of Eriptychius sp. (possibly a new species), Astraspis 

 sp., Pycnaspis sp. iudet. (see p. 8 and pi. 2, figs. 1-3) and sm'ely 

 also of other forms at present indeterminable as to genus. A par- 

 ticularly interesting specimen from this material is a large, keel-like 

 plate, ornamented on its external face with a system of broad, inoscu- 

 lating dentine ridges (pi. 3, figs. 1-4) ; it may, perhaps, belong to a new 

 representative of the Eiiptychiida. 



Bibliography 



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