POTOMAC AND KOOTENAI FAUNAS 345 



oi' Te.xu.s and New Mexico appear to be as well developed as those from 

 the Morrison. It can not be jnstly claimed that there is anything in the 

 Morrison in\ertebrates themselves that precludes their reference to an 

 earlier epoch than the Wealden. They do not offer any evidence on the 

 correlation of tlie Morrison with the Potomac group wliicli has been ad- 

 vocated on the basis of the vertebrate fauna. 



POTOMAC FAUNA 



The live species of invertebrates which W. B. Clark' has named from 

 I he I'olomac are apparently all distinct from Morrison species, but an 

 examination of the published figures shows that they are all so imper- 

 fectly preserved that even their generic reference is very doubtful. The 

 forms described are as follows : 



Unio patapscoensis Clark Viviparus arlinfjtonensis Clark 



Ci/rena marylandica Clark Bythinia arundelcnsis Clark 



All are from the Arundel formation except the Unio, which is from the 

 Patapsco. 



l^'urthci- cDiiiiuu-ison of the Morrison i]i\ertebrates shows that specific- 

 ally and as a fauna they are decidedly distinct from all othei- fresh-water 

 fannas that are found geographically or stratigraphically near them. The 

 faunas wliicli deserve mention in this connection are those of the Koote- 

 nai, the Bear River, and the Dakota. 



KOOTENAI FAUNA 



in ^[oniaiia the coal-bearing Kootenai formation has yielded non- 

 niai'iiic in\crtehrates at many localities, bnt tliey lunc not Ijeen thoroughly 

 collected noi' fully descrihcd. From a locality about "i miles southeast of 

 TTarlowton T luive dcscrihcih"' the following six species: 



Unio farri Goniobusis f silhcrUngi 



Unio douglassi Goniohasis ? ortmanni 



VivijHiius inontanaennis Campelonta harloivtoncnsis 



When these species were described their exact stratigraphic position 

 was not known, but it has since been determined that they came from 

 the Kootenai formation, which in the (Jreat Falls field has yielded similar 

 fonjis, though not so well |n-csci\cd, together with a Nerilina and some 

 other species. The so-called hakota fossils of the Yellowstone National 



*W. B. Clark: Lower Cretaceous, Maryland Geol. Survey, 1011, pp. 211-213. 

 * T. W. Stanton: A new fresh-water moUiiscan faunule from the Cretaceous of Mon- 

 tana. Proc. Am. I'hilos. Soc, vol. 43, 1903. pp. 188-199. 



