34 University of California Publications in Oeology [Vol. 12 



the interior and the Gulf provinces of the United States but also to 

 that of India, though neither to the extent of identity of species. 

 Of the two, the North American provinces are the more closely allied. 

 During the Neocene the Pacific Coast region became faunally more 

 distinct, which indicates that there was no intermigration of faunas 

 either with the eastern part of the United States or with India. 



CLIMATIC CONDITIONS INDICATED BY THE ECHINOID 



FAUNA 



Climatic conditions probably exercised a marked control over the 

 distribution of echinoids in past times, as at present, and from obser- 

 vations on the influence of temperature on the recent fauna, especially 

 that of the littoral zone, some conclusions may be reached as to the 

 previous ocean temperatures. Along the Pacific Coast Dendraster 

 exccntricus (Eschscholtz) , one of the most common Recent littoral 

 forms, has a geographic range from the Lower California coast to 

 Bering Sea. The genus Strongylocentrotus, similarly, has a wide dis- 

 tribution along the coast, but its different species are limited quite 

 distinctly by the variations in the temperature of the ocean. Other 

 Pacific Coast forms which show marked delimitations due to the tem- 

 perature conditions are the Atlantic form, ScuteUa parma (Lamarck), 

 which is confined entirely to the boreal waters from Puget Sound to 

 Kamchatka, and Mellita longifissa, which is a distinctly warm water 

 type and now found only in the Gulf of California and the Panama 

 region. The deeper water fauna is not reliable for temperature deter- 

 minations, Schizastcr and Spatangus, the more common fossil forms, 

 occurring in botli temperate and tropical zones of the world. 



From the fact that the pre-Miocene eehinoid faunas are largely of 

 the spatangoid type it is impossible to gain an idea as to the tempera- 

 ture conditions through their distribution without taking into consid- 

 eration the mulluscan life also, though the presence of Rhynchopygus 

 suggests a subtropical condition. An exception to this is Scutaster 

 andersoni Pack, the presence of which indicates that warm water pre- 

 vailed during the Oligocene. For the Lower Miocene the eehinoid 

 fauna indicates rather warm water as the scutellas, such as *S'. norrisi 

 (Pack), were large and highly specialized forms. Later in the Miocene 

 the genus Astrodapsis appeared and rapidly became abundant. Al- 

 though no species of this genus has survived to the present day, 



