Haynes: Fauna of the Upper Devonian in Montana. 27 



Faunal List of the Three Forks Formation. — Concluded. 



L. M. U. 



Ammonoidea. 



Plaiyclymenia americana Raymond 

 Plalyclymenia poly pleura Raymond 



Prolobites simplex Raymond 



Tornoceras crebrisepluin Raymond . 



T". douglassi Raymond 



Crinoid stems 



Bryozoa, cf. Edriotrypa sp.? 



lection made for the Museum of Comparative Zoology. In the faunal 

 list compiled by the writer, which immediately follows, only the species 

 identified by him are included, and their comparative abundance and 

 horizon are indicated by the letters R = very rare, r = rare, c = 

 common, and C = very common, in the column with the number of 

 the member in which they occur. The localities are not indicated on 

 the faunal list because no difference was found in the fauna of the 

 formation at the different localities. Most of the collecting was done 

 at Logan and in the east and west valleys north of Three Forks, but 

 enough specimens were collected from the other localities to show that 

 the same species occur at the same horizons throughout this region. 



This list of fossils identified by the writer from the Three Forks 

 formation shows among other things (i) that the ammonoids are 

 almost entirely limited to the lower and middle part of member 5, 

 and (2) that members i and 2 contain a fauna which is different in 

 most of its forms from that of the lower members, and is more like that 

 of the Madison limestone which overlies member i. The fauna of the 

 yellow sandstone and shale is considered by Dr. Raymond^^ to be 

 transitional between the Lower Mississippian fauna of the Madison 

 limestone and the Upper Devonian fauna of members 4 and 5 of the 

 Three Forks Formation. 



Dr. Schuchert^® has examined Dr. Raymond's specimens and notes 

 the presence of Syringothyris carteri and Spirifer cf. striatus, and con- 

 siders that this faunule is like that of the lower Louisiana limestone of 

 Pike County, Missouri. He therefore concludes that there was a 

 " break in deposition, clearly distinguishing the Devonic, both physic- 

 ally and faunally, from the Mississippic." 



" Raymond, Am. Jour, of Sci., Ser. IV, Vol. XXIII, 1907. P- nP- 

 15 Schuchert, Bull. Geol. Soc. Am., Vol. XX, 1910, p. 546. 



