26 University of California Publicatio-ns in Geology [Vol. 12 



INTRODUCTION 



The eehinoids have been recognized as a group of great import- 

 ance in the palaeontology and stratigraphy of the West Coast 

 Cretaceous and Tertiary formations, and their worth is being realized 

 as more detailed faunal studies are made and as more exact strati- 

 graphic work is done. In general, the eehinoids are of limited geo- 

 logic range, as their evolution proceeds rapidly. The species are easily 

 recognized, the individuals are often very abundant, and their state 

 of preservation is connnonly better than that of associated invertebrate 

 forms. These factors combined make the group of exceptional interest 

 for biologic studies, and of unusual importance in geologic correlation 

 and age determinations. 



The tirst study of the Cenozoic eehinoids of the Pacific Coast is 

 that of Conrad (1856), who described the genus Astrodapsis and the 

 species A. autiscUi. Remond (1863) recognized four important species. 

 No further contribution was made until Merriam (1898-1899) took 

 up the study of the evolution and geologic range of several species. 

 From this time on, the value of the group as an aid to stratigraphy 

 was realized, and during the decade between 1900 and 1910 valuable 

 contributions to the literature were made by Arnold (1907-1909), 

 Pack (1909), and Weaver (1908). A recent contribution of major 

 importance is that of Clark and Twitchell in their monograph, the 

 Mesozoic and Cenozoic Ecliinodermaia of the United States, which 

 includes descriptions of many California species. 



In beginning the present work it was intended to assemble the 

 eehinoids of California and adjacent regions in order to make the 

 available material more useful to the palaeontologist and the field 

 geologist. As the work progressed it became apparent that a consid- 

 erable part of the fauna had not been described in earlier papers 

 and that many of the described forms were in need of revision. It 

 was, therefore, necessary to make a thorough revision of the whole 

 echinoid fauna of the Pacific Coast in order to present a statement of 

 the geologic range and evolutionary sequence of the species. 



The first discussion in this paper deals with the geologic and 

 geographic ranges, the relationships of the Pacific Coast echinoid 

 faunas to those of other provinces, the climatic conditions indicated 

 by the echinoid faunas, and the phylogeny of the most important 

 genera ; the second part comprises systematic descriptions of the 



