J. P. SrnAth — Periodic Migrations. 223 



waters. Before the end of the Knoxville epoch, while the 

 Boreal forms still persisted, Lytoceras and Phylloceras, genera 

 that were never found in northern Europe and Asia, appeared 

 in the Cretaceous beds of the western coast of America. 

 These forms seem to have been endemic in the warm regions 

 of southern Europe and Asia, and their appearance marks a 

 resumption of interchange between India and America, around 

 the shore-line formed by closing the gap between Asia and 

 Alaska. In proof that the gap was really closed, it may be 

 said that the flora of the Knoxville beds and of the equivalent 

 Kootanie formation appears to indicate a warm temperate 

 climate,* which would mean that the cold current from the 

 Arctic Ocean had been cut off by a rise of the land. 



During the Lower Cretaceous Aucella made its way into the 

 Tropics, around the Pacific Ocean, so that its later occurrence 

 gives no evidence of southward extension of Boreal climatic 

 conditions.f 



Upper Cretaceous. — With the opening of the Horsetown 

 epoch all reminiscences of the Boreal fauna are gone, and the 

 Tropical character of the inhabitants of the sea on the western 

 coast of America is marked. A close affinity and even iden- 

 tity of species with the Indian fauna characterizes this epoch. 

 And it is noteworthy that the Puget Sound Horsetown and 

 Chico faunas are even more closely allied to those of India 

 than are those of California. Migration appears to have been 

 free between Asia and America, but the species did not all 

 range so far south as California, thus indicating the direction 

 from which they came. Of course, not all the marine forms 

 on the west coast of North America came from Asia, but the 

 Asiatic portion is the only one that we can trace to its source. 



The following species that occur in the Horsetown and 

 Lower Chico of western America are regarded by KossmatJ as 

 identical with species in southern India : 



Lytoceras Kayei Forbes. 



L. timotheanum Mayor. 



L. cola Forbes. 



L. indra Forbes. 



Hamites glaber Whiteaves. 

 Schloenbachia inflata Sowerby. 

 Acanthoceras Turneri White. 

 Pachydiscus otacodensis Stoliczka. 



P. arialurensis Stoliczka. 



Desmoceras diphylloides Forbes. 



*T. W. Stanton, Jour. Geol., v, 599, 1897. 



f Pompeckj, Ueber Aucellen und. Aucellen-ahnliche Formen, Neues Jahrb. 

 fur Min. etc., xiv, 348, 1901. 



% Beitr. Pal. und Geol. Oesterreich-Ungarns und des Orients, ix, Parts 3 

 and 4, 1895. 



