LOGAN : FREEZE-OUT HILLS OF WYOMING. 119 



found to have still closer affinities to the American interior fauna. 

 The Jurassic faunas of America have also received many additions at 

 the hands of the American paleontoloii^ists Gabb, Hyatt, White, Meek, 

 Whitfield, Whiteaves, Smith, and Stanton. From a study of the evo- 

 lution and distribution of Jurassic faunas, it has developed that the 

 American interior fauna is largely a heterochthonous fauna which has 

 migrated from northern Eurasia. As a whole it is radically ditferent 

 from its equivalent in time as it is represented in the Pacific deposits 

 of California. 



The following comparison of forms which seem so closely allied as 

 to deserve to be called varieties of the same species will serve to show 

 the close affinity of the fauna of the interior to the fauna of Eurasia : 



Belemnites panderamis d"Orb = Belemnites devsus Mk. 



Astarte duboisianus (V Orb = Astarte packardi White. 



Pentacrinus pentagonifes Golldf . ... = Pentacrinus astericus Mk. 



Avicula tenuicostata Roem = A vicula niucronata Mk. 



Goniomija dtibo/s d'Orb = Goniomya montanaensis Mk. 



Card/oceras cordalus Sowerby = Ccirdioceras cordiforme Mk. 



Ostrea duriscula d'Orb ^^ Ostrea densa, n. sp. 



Gryphea calceola Quen =; Gryphaa nebrasceuHis Mk. 



The fauna taken as a whole exhibits the close relationship in a 

 much more forcible manner than the comparison of a few sj^ecies can 

 show. 



The Jurassic fauna of the whole interior is essentially the same as 

 the fauna of the Black Hills, which Neumayr, in his Geographische 

 Verbreitung Juraformation, shows to be a northern fauna closely re- 

 lated to that of northern Eurasia. To explain the joresence of this 

 northern fauna in the interior and its dissimilarity to the Pacific 

 fauna of California, he postulates the southern extension of an arm 

 of the Arctic ocean at a point east of the Rocky mountains and the 

 existence of a land barrier between the two provinces. 



DESCRIPTION OF SPECIES. 



In order to give a comprehensive idea of Jurassic fauna of the 

 Freeze-out Hills, I have brought together and described all of the 

 species found there, although a large part of them are already known 

 Prom other localities. Many of the specimens described here have 

 been recognized in the Black Hills, in the Yellowstone national park, 

 )n Wind river, and on Queen Charlotte islands. 

 I'enfffci'inus (isff^rtrHs Meek and Havden. Plate XXV, figs. 4, 5, 6, 7. 

 Many fragments of crinoid stems were collected from a thin stratum 

 )f arenaceous limestone occurring in the clay of No. 15. Fragments 

 vtre also found in the nodules of No. 13. These forms are all referred 

 () the species Pentacrinus astericus. 

 The stems are composed of small pentagonal joints. The margins 



