1915] 



Clark: Fauna of the San Pablo Group 



403 



Scutella gabbii is found at the base of the section. The most com- 

 mon species found with Scutella gabbii or in the same horizon are 

 Dosinia merriami. Modiolus gabbi, Ostrea bourgeoisii, Pecten crassi- 

 cardo, Siliqua lueida, Spisula abscissa, Spisula albaria, Spisula cat ill i- 

 formis, Cerithiopsis turneri and Natica (Euspira) kirhensis. 



The beds of the upper portion of the lower San Pablo contain a 

 number of species that do not appear in the basal beds, the most com- 

 mon of which are Mytilus coalingensis, n. var.?, Sanguinolaria alata, 

 Calyptraea diabloensis and Littorina remondii. Calyptraea diabloensis, 

 Mytilus coalingensis n. var ? and Sanguinolaria alata appear to be 

 characteristic of this horizon ; all occur also on the south side of the 

 Mount Diablo anticline associated with Astrodapsis tumidus subsp. 

 cierboensis and Scutella pabloensis, together with an assemblage of 

 species that is very similar to that on the north side of the mountain. 

 Thus the two lower minor faunal zones of division A of the Bay 

 Section are also recognized on the north side of Mount Diablo. 



The fauna of the upper San Pablo in this area is to be correlated 

 with that of division B of the San Pablo Bay section. The character- 

 istic species are Astrodapsis whitneyi, Cyrena (Corbicula) calif ornica, 

 and Trophon carisaensis. Here, as in the San Pablo Bay section, the 

 great abundance of Cyrena (Corbicula) calif ornica in the upper part 

 of the group indicates brackish-water or estuarine conditions. 



