144 



University of California Publications in Geology [Vol. 13 



Number of determinable species 6412 



Number of species so far recognized only in the Briones 21 or 32.8 % 



Number of species that extend into the San Pablo 41 or 64.0% 



Number of species that extend into the Etchegoin (Pliocene) 19 or 29.7% 



Number of Recent species occurring in the Briones 12 or 18.8% 



Number of species that extend into the Monterey group (Vaqueros 



and Temblor) : 12 or 18.8% 



Number of species that extend into the Oligocene 2 or 3.1% 



Number of species peculiar to the Briones and San Pablo 20 or 31.2% 



Number of species peculiar to the Briones and the Monterey group 1 or 1.5% 



RELATION OF THE BRIONES FAUNA TO THE 

 MONTEREY FAUNA 

 A study of the known fauna of the Briones formation indicates 

 that it has a much closer relationship to the San Pablo than to the 

 Monterey. Twelve out of the sixty-four determinable species (18.8 

 per cent) extend into the Monterey, while forty-one species or 64 per 

 cent occur in the San Pablo. Of the twelve species that extend into 

 the Monterey, ten are known to occur in the San Pablo, one (Tellina 

 oregonensis Conrad) occurs in the Oligocene, and only one (Chione 

 panzana Anderson and Martin) 13 is peculiar to the Briones and the 

 Monterey. Since only one (or possibly two) species out of a deter- 

 minable fauna of sixty-four species is peculiar to these two formations, 

 it appears that the Briones fauna is distinct from that of the Monterey. 



RELATION OF THE BRIONES FAUNA TO THE 

 SAN PABLO FAUNA 

 Of the forty-three known Briones species that extend into other 

 formations forty-one occur in the San Pablo. Of these, twenty are 

 peculiar to the Briones and to the San Pablo. They are : 



Dosinia arnoldi Clark 



Dosinia merriami Clark 



Dosinia merriami occidentalis Clark 



Macoma andersoni Clark 



Mulinia pabloensis Packard 



Ostrea bourgeoisi Eemond 



Pecten bilineatus Clark 



Pecten erassicardo (Conrad) 



Pecten raymondi Clark 



Pecten raymondi brionianus n. var. 



Tivela diabloensis Clark 

 Venus martini Clark 

 Zirphaea dentata Gabb 

 Astralium raymondi Clark 

 Cancellaria pabloensis Clark 

 Ficus stanfordensis Arnold 

 Natica arnoldi Clark 

 Natica kirkensis Clark 

 Natica pabloensis Clark 

 Trophon gracilis clarki, nov. nom. 



12 The large number of indeterminable species is chiefly due to the generally 

 poor preservation. A rather high percentage of the Briones fossils consists of 

 casts or molds. 



is Nassa whitneyi, n. sp., may possibly extend into the Monterey, but even if 

 it did, there would then be only two species peculiar to these two formations. 



