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University of California Publications in Geology [Vol. 8 



appears. This species is found through a large part of division A. The 

 third minor faunal zone described from division A of the San Pablo 

 Bay section has not been recognized in any other section. 



The species associated with Astrodapsis tumidus, subsp. cierboensis 

 both here and in the San Pablo Bay section, believed to be characteristic 

 of division A. are Scutella pabloensis, Mytilus coalingensis Arnold, 

 n. var. ?, Spisula abscissa, Tivela diabloensis, Chrysodomus pabloensis. 

 One of the most common species found in this zone and one which is 

 believed to be at least locally characteristic of it, is Mytilus coalingensis, 

 n. var? It occurs with an assemblage of species very similar to that 

 with which it is found on the north side of the mountain. Some of 

 these species are Macrocallista uewcombiana, Macoma nasuta, Ostrea 

 bourgeoisie, Paphia staminea, Pecten crassicardo, Pecten raymondi, 

 Saxidomus nuttallii, Scliizothaerus nuttallii, and Calyptraea diablo- 

 ensis. 



Division B. — From the 200 to 300 feet of sandstones just beneath 

 the lowest and most persistent leaf-bearing shale of the Sycamore and 

 Tassajero Creek sections, a very good fauna was obtained, including 

 two species of sea-urchins, Astrodapsis ivhitneyi and Astrodapsis 

 tumidus, and many mollusks. Some of the common mollusks are 

 Chione pabloensis, Crypiomya ovalis, Dosinia arnoldi, Dosinia mer- 

 riami var. occidental-is, Macoma secta, Macoma nasuta, Macoma ander- 

 soni, Modiolus gabbi, Modiolus directus, Mulinia densata, Pecten 

 raymondi, Pecten crassicardo, Pinna alamedensis, Venus martini, 

 Astralium raymondi, Natica (Neverita) pabloensis, Cancellaria pab- 

 loensis, Trophon carisaensis, and Trophon lawsoni. Mulinia densata 

 makes its first appearance in these lower sandstones of division B, 

 a fact worthy of especial note. This species has not been found in 

 the lower part of any section of the San Pablo group in this part of 

 the state. One bed two or three feet thick in these sandstones is made 

 up almost entirely of the shells of this species, and the layer is per- 

 sistent for a number of miles along the strike. 



The typical Astrodapsis ivhitneyi was not found in the beds just 

 above the lowest shale member of the Tassajero or Sycamore Canon 

 sections. The fauna found above this shale, though not large, in- 

 cludes a number of species that have not been found below the shale. 

 Of these Tivela gabbi and Nassa pabloensis may prove to be char- 

 acteristic of the upper part of the group. 



In the Walnut Creek section on the west side of Shell Kidge there 

 was found at one horizon a fairly large fauna. In this vicinity (Shell 

 Eidge) the lower part of division B is composed of fairly coarse sand- 



