I 



364 University of California. [Vol. i. 



teeth of a lizard closely related to Lacerta, were also found in this 

 stratum. In a semi-lignitic layer a short distance above that con- 

 taining Limiura, etc., numerous but imperfect plant remains* were 

 found. 



The rodent remains, consisting of the greater portion of a skull 

 with the upper molars and incisors, were imbedded in a stratum of 

 hardened clay immediately below the lignite. 



Dr. Charles Palache was directly instrumental in the discovery 

 of the skull, as the writer's first visit to the fresh-water beds was 

 made under his guidance. 



HISTORY OF THE CASTORID/E. 



The beaver family reached its maximum development, in point 

 of number of genera and species, in the middle Tertiary, and is rep- 

 resented at the present time by a single genus and species, Castor 

 fiber, the beaver. The oldest representatives of the family known 

 are found in the Lower Miocene, three species of the genus Stcneo- 

 fibcr occurring at that horizon in America and one in Europe. This 

 genus became extinct in the Middle Miocene of North America, but 

 continues into the Upper Miocene and possibly Pliocene, Steneo- 

 fiber (Chalicomys) sigmodus of Europe. 



In the uppermost Miocene or lowest Pliocene (Loup Fork Beds) 

 of North America two new genera, Eucastor and Mylagaulus, appear, 

 representing new types of beaver, in which reduction in the number 

 of molars has taken place. These types seem to have at least a dis- 

 tant relative in Stcneofibcr {Clialieomys) sigmodus of the European 

 Pliocene. 



The modern beaver, Castor, appears in the upper Pliocene of 

 Europe and America, being accompanied in Europe by the genus 

 Trogontherium, the largest representative of the family. Castor 

 continues through the post-Pliocene up to the recent period, but its 

 relative Trogontherium became extinct in the Quaternary. Castor 



* These plant remains, though imperfect, could, in part, be determined by 

 an expert in the paleobotany of the Coast Range Tertiaries. They may at 

 some future time be of value in correlating the Pliocene of Berkeley with the 

 more fossiliferous and better known Pliocene around Mt. Diablo. The latter 

 contains, aside from a rich marine fauna, abundant plant material, which has 

 been partially worked up. 



