82 University of California Publications in Geology [Vol. 11 



side. Besides this, there is a column for each of the formations de- 

 scribed above, in which is indicated whether a species is rare or 

 common, or whether it has been found only in that particular 

 horizon. 63 



Comparisons of Fauna of San Lorenzo West of Mount Diablo with that 

 Found in the Lower Part of Monterey of the Same Area 



The distinctness of the San Lorenzo fauna from that of the Lower 

 Miocene will be discussed in considerable detail in a later part of this 

 paper. The fauna found in the lower Monterey of the Concord 

 Quadrangle belongs to what is generally known as the Temblor hori- 

 zon of the Lower Miocene, the Turritella ocoyana zone. There is very 

 little in common between this fauna and that of the San Lorenzo 

 series. 



The following are some of the most important described species 

 found in the basal beds of the Monterey of the Concord Quadrangle : 



Area montereyana Osmont Spisula eatilliformis (Conrad) 

 Chione cf. temblorensis Anderson Spisula selbyensis Packard 



Marcia oregonensis (Conrad) Tellina aretata Conrad 



Mulinia densata Conrad Thracia trapezoides Conrad 



Ostrea n. sp. aff. titan Conrad Agasoma barkernianum Cooper 



Pandora scapha Gabb Crepidula princeps (Conrad) 



Panope cf. estrellana Conrad Fusinus stanfordensis (Arnold) 



Peeten andersoni Arnold Natica (Neverita) recluziana 

 Pecten cf. nevadensis Conrad (Arnold) 



Of the species listed above, the only ones which have been found 

 in the San Lorenzo beds of this region are Panope cf. estrellana and 

 Natica (Neverita) recluziana. 



Possibility of Faunal Zones in San Lorenzo to the West of Mount Diablo 



The fauna from the different horizons of the San Lorenzo series to 

 the west of Mount Diablo, taken as a whole, appears to be fairly 

 homogeneous. A considerable number of species extend from the lower 

 beds into the upper, among which are several highly ornamented gas- 

 tropods such as Agasoma gravidum, Calliostoma lawsoni, Cancellaria 

 andersoni, Fusinus hecoxi, Molopophorus biplicatus, Turris thurston- 

 ensis, Turritella porterensis sobrantensis, etc. On the other hand, as 

 indicated in the list above, there are a number of species which have 



63 The f ollowing abbreviations are used to indicate this information : C, com- 

 mon ; E, rare ; E, characteristic, that is, so far not found in higher or lower 

 horizons. 



