1915] 



Clark: Fauna of the San Pablo Group 



425 



appears to be restricted within a thickness of about two hundred and 

 fifty feet of strata ; and this part of the section is designated the Astro- 

 dapsis whitneyi zone. Astrodapsis tumidus ranges well up toward the 

 top of the group. (4) On the south side of the Mount Diablo anticline, 

 the beds immediately above the Astrodapsis whitneyi zone and above 

 the lowest persistent shale of division B of that section, contain a few 

 molluscan species which may prove to be characteristic of this horizon. 

 At a few localities on the south side of Mount Diablo (in the upper 

 beds of the San Pablo, above the so-called river conglomerates), a still 

 higher minor faunal zone is indicated by the presence of a large variety 

 of Astrodapsis tumidus. 



The two major faunal zones in the series are separable not only on 

 the basis of the sea-urchins, but also on the basis of the molluscan 

 fauna. There are some differences between the molluscan faunas in 

 some of the minor faunal zones as has been shown in the description 

 of the fauna from the south side of the Mount Diablo anticline ; those 

 differences, however, are not so great or well founded as those between 

 the two major zones. 



The following species present in the lower zone have not been 

 found in the upper zone, or in any other formation strati graphically 

 above the San Pablo. Those marked with an asterisk have not been 

 found in more than one section. 



Seutella pabloensis Kew. 

 Astrodapsis tumidus 



subsp. cierboensis Kew 

 *Asterias remondi Gabb. 

 Dosinia merriami, n. sp. 

 Mytilus coalingensis Arnold, 



n. var? 



Ostrea bourgeoisii Eemond. 

 *Peeten cierboensis, n. sp. 

 *Pecten weaveri, n. sp. 

 *Pitaria behri, n. sp. 

 *Pitaria stalderi, n. sp. 



Sanguinolaria alata Gabb. 



Spisula abscissa Gabb. 



Tivela diabloensis, n. sp. 

 *Tivela diabloensis var. angulatum, 



n. var. 

 *Bursa carinatus, n. sp. 

 *Cerithiopsis turneri, n. sp. 

 *Columbella (Astyris) kirkensis, 



n. sp. 



Chrysodomus pabloensis, n. sp. 

 *Ficus, cf. stanfordensis Arnold. 

 *Littorina remondii Gabb. 

 *Murex selbyensis, n. sp. 

 *Trophon gracilis Perry, 



var. pabloensis, n. var. 

 'Trophon dickersoni, n. sp. 



The following species from the upper major faunal zone have not 

 been found in the lower zone and have not been reported from any 

 formation above the San Pablo group. Those marked with an asterisk 

 have not been found in more than one section. 



