Mbrriam.] Distribution of the Neocene Sea-urchins. 



i I I 



the Post-pliocene. It is not impossible, however, that it belongs 

 also to the top of the Pliocene, since the line drawn between the 

 Quaternary and the Pliocene near the top of the clill section is to 

 some extent an arbitrary one. 



Besides the occurrence at Seven-mile Beach, A. cxceiitncits is 

 known from the Quaternary of Santa Barbara and San Pedro and 

 also from San Fernando, Los Angeles County. At the last-named 

 locality it is said to be in the Pliocene. Satisfactory information 

 regarding these occurrences has not been obtained by the Writer, 

 but, judging from the state of preservation of the specimens 

 examined, they are all either of late Pliocene or of Quaternary age. 



Scutella interlineata is fairly common throughout the greater 

 portion of the Merced. It is not rare near the base of the series 

 at the typical locality, on Seven-mile Beach, and is found at intervals 

 up to a point considerably beyond the middle of the section. It is 

 known also from Humboldt County, California, where it is asso- 

 ciated with a fauna similar to and probably of the same age as 

 ■that of the lower portion of the Merced near San Francisco. 



The remaining species which have been considered as Pliocene, 

 viz., Astrodapsis WJiitneyi and A. tumidus* occur along with Scittclla 

 {Clypcastcr) Gabbi in a series of strata which is well developed 

 on the south shore of San Pablo Bay, at Kirker's Pass north of 

 Mt. Diablo, and in the hills to the south and west of Mt. Diablo. 

 At these places they are associateel with a fauna not known 

 at other horizons, containing among other characteristic forms, 

 Pscudocarditm Gabbi, Pcctcn Pabloensis, Pinna . llamedensis, Mulinia 

 densata, Trochita n. sp., Littorina Remondi, and Trophon pon- 

 dcrosum. 



Within this series the Scittclla, wherever present, occupies a 

 lower horizon than Astrodapsis. In a remarkably well-exposed 

 cliff section, near the Union Oil Refinery, on the south shore of 

 San Pablo Bay, the best-known example of the zonal distribution 

 oi these sea-urchins is very clearly shown. At this point the 

 strata are standing almost vertically, exposing a thickness of nearly 



* A. tumidus occurs also in the southern part of the state, in Santa Barbara 

 and Ventura Counties. 



