128 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Sek. 



Thyasira bisecta. Fewer tropical genera than in Eocene. 

 Faunas already provincial, but climatic zones not yet definitely 

 established. 



MIOCENE. 



Numerous Pecten : Lyropecten, Amusium, Patinopecten, 

 Janira, Spondylus; VeneridcB abundant: Chione ancestral to 

 modern groups, Amiantis, Dosinia, Tivcla; giant Ostrea; giant 

 Cardium; Pinna; Avicula; Agasoma, Astrcsa, giant Conus, 

 Ficus, Mitra, Molopophorus, Miopleionia, Nassa, Oliva, Pris- 

 cofusus, Purpura, Trophon, Turritella, Rapana, Astrodapsis, 

 Clypeaster, Dendraster, Scutella. Disappearance in later 

 Miocene of most of the tropical genera, and reduction in size 

 of most of the remaining ones. Notable exception to this is 

 the great increase in the size of the pectens and oysters, which 

 are veritable giants. Few extinct genera: Molopophorus, 

 Agasoma, Miopleionia, Astrodapsis. Climatic zones developed, 

 but not sharply defined. Faunas distinctly provincial. Many 

 modem species. 



PLIOCENE. 



Dwarf V enericardia. Area, Cardium, Chione, Spisula, 

 Patinopecten, Chlamys, Janira, Paphia; Fusus, Chrysodomus, 

 Purpura, Nassa, Dendraster. Climatic zones already sharply 

 defined in lower Pliocene, with Miopleionia, giant Chryso- 

 domus, Buccinum, Volutopsius, and Patinopecten in northern 

 California; and Lyropecten, Janira, abundant Chione, Dosinia, 

 Ficus, Murex, and giant Conus in southern California. The 

 Wildcat fauna of Humboldt County, California, was cold 

 temperate, the Purisima of middle California was warm tem- 

 perate, while the Fernando of southern California was sub- 

 tropical, all contemporaneous. 



Miopleionia and Astrodapsis are the only extinct genera, but 

 there are many now extinct in the Californian province. More 

 than half of the Pliocene species are still living. 



QUATERNARY. 



Fauna like the Recent, but with rapidly shifting climatic 

 zones, northern species ranging southward in lower Pleistocene, 

 and southern species ranging northward in upper Pleistocene. 

 Few extinct species, but many extinct locally. 



