1 I 2 



Liniversity of California. 



[Vol. 2. 



fifteen hundred feet. At the bottom or north side of the section 

 Scutella is very abundant and Astrodapsis is absent. Two or 

 three hundred feet farther up Scutella disappears and Astrodapsis 

 appears. From that point to a distance of nearly one thousand 

 feet higher Astrodapsis is abundant, Scutella apparently not pass- 

 ing beyond the stratum at which Astrodapsis appears. The two 

 species are, however, abundant in beds less than ten feet apart, 

 and may be found to overlap. At other localities in this forma- 

 tion the same sequence of genera was observed. The exact 

 relations which the two species of Astrodapsis bear to each other 

 in time have not yet been determined, but tumidus is possibly 

 the older. The Astrodapsis forms are perhaps the more char- 

 acteristic of the formation, as the lower beds with Scutella are 

 sometimes absent, while the upper and much thicker Astrodapsis 

 beds are usually present. 



The third species of Astrodapsis, viz., A/itiselli, which has been 

 supposed to be Miocene, is possibly identical with one of the 

 other two forms. It occurs* in San Luis Obispo and Kern Coun- 

 ties, where it is associated with a fauna much like that found 

 with A. tumidus and Whitneyi. 



Of the remaining forms referred to the Miocene, Ecliiiiarachnius 

 [Scutella) Gibbsi is known from Neocene strata, near Kuena 

 Vista Lake, Kern County.| It is also listed by Ashley* from 

 his transition beds near Santa Cruz, where it is said to be asso- 

 ciated with 5. interliueata. 



The oldest of the Neocene sea-urchins, Clypeaster? (Echiua- 

 rachuius) Bretveriamts is a common species in the upper portion 

 of a voluminous series in Contra Costa County, generally recog- 

 nized as Miocene, which at Walnut Creek, near Mt. Diablo, 

 underlies the formation containing Astrodapsis. 



From what has already been stated, regarding the distribu- 

 tion of the Neocene and Quaternary Echini, it will be seen that 

 there are, in the middle Californian region at least four distinct 

 sea-urchin horizons above the middle of the Miocene. The zone 



- Pacific R. R. Rep., Vol. 7, p. 196. 



tProc. Cal. Acad. Sc., Vol. Ill, 1863-67, p. 13. Remoiid. 

 % Proc. Cal. Acad. Sc., Second Ser., Vol. V, p. 328. 



