SOUTHERN CALIFORNIA ACADEMY. OF SCIENCES. ^t 



Desmostylus hesperus, gen. et sp. nov. 

 "The remains known of the present species indicate an ani- 

 mal about fifteen feet (m.4.5)in length, and of robust proportions. 

 The most characteristic parts preserved are the molar; teeth, 

 which are composed of a number of vertical columns, closely 

 pressed together, and in adult animals, firmly united at their 

 bases. These columns are thickly invested with enamel, which 

 is rugose externally. Inside the enamel, is a body of dentine, 

 in which there is a central cavity. * * * 



The specimen figured is apparently the posterior portion of 

 a molar tooth. * * * * One of the best preserved speci- 

 mens found with these teeth is a lumbar vertebra, which is 

 noticeable for the extreme flatness of its articular surfaces. 



"The known remains of this animal are from Alameda 

 county, California, and are preserved in the museum of Yale 

 College. The type specimen was found by Dr. L. G. Yates." 



In many of the fragments of the teeth of the above described 

 animal found by me the individual susps were generally well 

 worn, some of them to one-half of their original length, and 

 when so worn the grinding surface was always smooth, and 

 had a slightly convex surface, so that I cannot agree with my 

 friend, Prof. Marsh, that "Before being worn, they have their 

 summits smooth and convex, but after some use, the center of 

 each column presents a rounded elevation, well shown in the 

 figures." 



In the illustration. Figs, i and 2 show the surface of the 

 worn portion, and Fig. 3 the outline of the worn portion on the 

 outer edge of the tooth. 



Professor Dana believed that the Cretaceous Mollusca of 

 this Coast continued down into the earlier Tertiary, as there 

 was no great or important convulsion to destroy them until the 

 Middle Eocene ; Thus the theoretical dividing line between the 

 Upper or Later Cretaceous and the Lower or Earlier Tertiary 

 was bridged over, as was suggested by Dr. J- G. Cooper, and 

 is not apparent. The marked unconformity of the Miocene witR 

 the earlier formations show that some great changes took place 

 about the time of the inauguration of the Miocene, or Middle 

 Tertiary. 



During the Miocene Period very little of the land we call 

 California was above the level of the ocean, a fact which ex- 

 plains the absence of remains of land animals of the period, 

 found in such abundance in Oregon, Wyoming and Utah ; That 

 portion of California lying south of the Bay of San Francisco, 

 and from the Pacific shore to the western foot of the Sierras 

 was an almost unbroken sea. 



In a paper published by the California Academy of Sciences 

 in 1874 Dr. Cooper says : "The fossil evidence which we pos- 

 •sess relating to the Miocene epoch in California is, however, 



