1915] 



Clark: Fauna of the San Pablo Group 



401 



Spisula abscissa, Tivela diabloensis, Chrysodomus pabloensis, Murex 

 selbyensis. 



Division B. — The most fossiliferous portion of division B is in the 

 sandstones just above the band of shale already described. Over forty 

 species were obtained from this zone, a large number of which have 

 never been found in division A or in the lower portion of any other 

 section of the San Pablo Group. The species that appear to be char- 

 acteristic of the zone and which are found in more than one section are 

 Astrodapsis tumidus, Acila conradi, Cyrena calif ornica, Macoma pab- 

 loensis, Macoma andersoni, Mytilus perrini, Mya dickersoni, Pinna 

 alamedensis, Pecten pabloensis, Pecten bilineatus, Tivela gabbi, Natica 

 (Neverita) arnoldi and Trophon carisaensis. 



Astrodapsis tumidus is found in the beds above the shale in great 

 abundance, and in some places the coarser sandstones are made up 

 almost entirely of the individuals of this species. The Pecten beds 

 described by Dr. Newberry in the Pacific Railroad Reports are found 

 in this horizon and the types of Pecten pabloensis Conrad, Pecten 

 bilineatus, n. sp., Pecten holwayi, n. sp., were obtained from them. 

 Pecten crassicardo is also found at this locality (Univ. Calif. Loc. 

 1632). Other localities are nos. 1613, 1614, and 1615. 



The fauna found below the shale member in the upper San Pablo is 

 not essentially different from that above with the exception of a few 

 species, including Diplodonta parilis, Sanguinolaria nuttalli, Tellina 

 salmonea and Trophon lawsoni. 



A noteworthy fact in connection with the discussion of the fauna 

 of division B is that in at least two zones we have estuarine or brackish- 

 water deposits, as is evidenced by the presence in great abundance of 

 the forms of Cyrena (Corbicula) and Mya, associated with genera 

 which at the present time are found living under either estuarine or 

 marine conditions. The first horizon of estuarine or brackish-water 

 deposits is the shale member. In this the species Cyrena (Corbicula) 

 calif ornica was found, together with leaf impressions. The other zone 

 is near the top of the group in medium fine sandstones. At locality 

 1617 in this zone certain layers are composed almost entirely of the 

 shells of Cyrena (Corbicida) calif ornica and Mya dickersoni. 



