1 915 ] Clark: Occurrence of OUgocene in the Contra Costa Hills 15 



Pecten, sp.? 



Phacoides acutilineatus (Conrad) 

 Pitaria, n. sp. 

 Psammobia, sp. 



Solen, n. sp. aff. parallelus Gabb 

 Solen curtus Conrad 

 Spisula occidentalis (Gabb) 

 Spisula ramonensis Packard MS. 

 Spisula, sp.? 



Tellina oregonensis Conrad 

 Tellina, sp.? 

 Tellina, n. sp. 



Tellina lorenzoensis Arnold 

 Thracia condoni, Dall 

 Thracia, n. sp. 

 Yoldia, n. sp. 

 Yoldia, sp.? 

 Gasteropoda 



Agasoma acuminatum Anderson 



and Martin 

 Agasoma gravidnm (Gabb) 

 Ancillaria fishi Gabb 

 Bursa mathewsoni (Gabb) 

 Calliostoma, n. sp. 

 Columbella, n. sp. 

 Chrysodomus, n. sp. 

 Chrysodomus, n. sp. 

 Crepidula praerupta Conrad 

 Cerithium, n. sp. 

 Calyptraea excentrica (Gabb) 

 Calyptraea radiata (Lamarck) 

 Cancellaria condoni Anderson 

 Epitonium, n. sp. 

 Epitonium, sp.? 

 Eusinus (Priscofusus) hecoxi 



Arnold 

 Haminea, sp.? 

 Mioplenia, sp.? 



Molopophorus biplicatus Gabb 

 Molopophorus gabbi Dall 

 Murex (Ocinebra), n. sp. 

 Natiea (Neverita) recluziana 

 Petit 



Natica (Neverita), cf. callosa 



Gabb 

 Natica, n. sp. 

 Natiea (Euspira), n. sp. 

 Natica (Neverita), n. sp. 

 Neptunea recurva Gabb 

 Olivella, n. sp. 



Olivella, cf. pedroana Conrad 



Phalium, n. sp. 



Sinum seopnlosum (Conrad) 



Strepsidura, sp. 



Thais, n. sp. 



Turbinella, sp.? 



Turritella porterensis Weaver 



Turris, n. sp., A. 



Turris, n. sp., B. 



Turris, sp.? 

 Scaphopoda 



Dentalium, n. sp. 



Dentalium petricola Conrad 



Dentalium, cf. stramineum Gabb 

 Cephalopoda 



Aturia, sp.? 

 Crustacea 



Balanus, sp.? 

 Anthozoa 



Siderastrea, n. sp. 

 Amphiueura 



One anterior plate of chiton 

 Eehinodermata 



Linthia californica Weaver 



RELATION OP THE AGASOMA GRAV1DUM ZONE TO THE LOWER 

 MIOCENE OP SOUTHERN CALIFORNIA 



Before considering the problem of the correlation of the Agasoma 

 gravidum zone, it is desirable to outline the classification of the marine 

 Neocene of the Californian area. 



The Neocene of California is divisible into two parts by a strati- 

 graphic break, which occurs somewhere between Middle and Upper 

 Miocene. This interruption has been referred to by Arnold as "the 

 most widespread and important period of diastrophism in the Ter- 

 tian history of the Pacific Coast. . . . Its effects are visible from 

 Puget Sound to Southern California ; it is marked by much readjust- 

 ment, by local faulting and folding, as by general movements of 

 elevation and subsidence." 15 



is Arnold, Ralph, Environment of the Tertiary Faunas of the Pacific Coast, 

 in Willis and Salisbury, Outline of Geologic History, p. 241, 1910. 



