458 University of California Publications in Zoology [Vol. 12 



Upper Oligocene, it should be remarked, Steneofiber had attained a 

 world-wide distribution. It was replaced, in the Lower and Middle 

 Miocene of Europe, by Chalicomys, which died out during the Plio- 

 cene. Matthew derived the phylogenetic side-line represented by 

 Hystricops of the North American Miocene and Pliocene from Steneo- 

 fiber. 



Little is known concerning the genus Euhapsis, a supposed cas- 

 torid genus which occurred in North America during Upper Oligo- 

 cene. 



Eucastor or Dipoides of Upper Miocene, as well as the genus 

 Castor itself, which first appeared in that period, are probably also 

 descended from Steneofiber. Eucastor, which was, like Steneofiber, 

 about the size of a marmot, is first found in the North American 

 Hipparion and Procamelus zones (Upper Miocene) and ranges into 

 the Pliocene. Sigmogomphius (Merriam, J. C, 1896, p. 365) from 

 the Pliocene near Berkeley, California, and Dipoides, from the Plio- 

 cene of Asia, are closely related to if not congeneric with it. Appar- 

 ently the Eucastor-Dipoides stock appeared first in North America, 

 spreading later into Eurasia. The Eucastor line soon ran out in 

 the Old World, while in North America it appears to have given rise 

 to the Pleistocene family Castoroididae with its characteristic genus 

 Castoroides. 



The earliest species of the European genus Trogonthcrium ap- 

 peared in the Upper Pliocene, being there represented by teeth much 

 smaller than those of its successor in the Pleistocene, Trogonthcrium 

 cuvieri, the giant beaver of Europe, which was about one-fifth larger 

 than the beaver of modern times. This genus coexisted in Europe 

 with Castor, but died out at the close of what Osborn calls the First 

 Faunal Subzone of the Second Pleistocene Fauna. 



The largest species of the Pleistocene Castoridcs of North America 

 attained the size of a black bear, and was, like the big European 

 Trogontherium, preceded by a smaller form. 



The genus Castor, on the basis of evidence now at hand, appeared 

 somewhat earlier in Europe than in America. The Pontian Upper 

 Miocene deposits are the first in Europe in which Castor has been 

 discovered. The recent discovery (Kellogg, 1911, p. 401) of a beaver- 

 tooth in the Pliocene of California seems to indicate that it soon 

 attained a distribution embracing both continents. Castor is found 

 in Pliocene and Pleistocene European formations, and is widespread 

 in North American Pleistocene. It is lacking from the Pliocene and 



