26 CALIFORNIA ACADEMY OF SCIENCES rPROC. 4th Ser. 



gions to the Pliocene are roughly adaptable to the Miocene, and 

 similarly the percentages which apply in the temperate regions 

 to the Pleistocene are apparently those of the Pliocene of the 

 tropics. The reasons for this apparent lack of faunal differen- 

 tiation during the Tertiary in the tropics are those due to uni- 

 formity of temperature, salinity, food, and other life essentials. 

 From another viewpoint the rate of evolution of Gastropoda 

 and Pelecypoda in the tropics during the Tertiary was far less 

 than during this same time in the more rigorous environs of 

 the temperate zones. The tropical or sub-tropical faunas of 

 the Eocene of the Pacific Coast of North America exhibit but 

 slight differences compared to the faunas of Miocene and Plio- 

 cene age of this same region, and the writer ascribes this to 

 uniformity of life conditions which prevailed during Eocene 

 time. The amount of faunal change must not be used as a 

 measure of time in the whole of the Tertiary, but differently 

 marked scales are necessary for measurement in tropical and 

 sub-tropical faunas of the Eocene and Oligocene than for the 

 Miocene, Pliocene, and Pleistocene. It is particularly note- 

 worthy that the Japanese paleontologists are now searching 

 for comparisons with the Pacific Coast of North America and 

 Australia rather than with Europe. In other words, many 

 problems of the tropical Orient will be solved only when condi- 

 tions on both sides of the Pacific become better known. 



