Geol.— VOL. I.] MERRIAM— TERTIARY SEA-URCHINS. 165 



Quaternary Echinarachnms excentricus^ 



Merced 



San Pablo 



SctUella mterlincata 



(F) Echinarachnms Gibbsi 



Astrodapsis Whitneyi 



Astrodai)sis tumidus i,y, 



SciiteUa Gabbi 



\ 



\ ? 

 \ • 

 \ 



Contra Costa County Clypeaster {?) Breweriamis 

 Miocene 



Tejon 

 Martinez 



Schizastcr LeContci 



Ambulacra broad, sunken; anterior laterals reaching a little more than half 

 way to the margin; posterior laterals very short, less than half the length of 

 the anterior pair, sometimes almost circular in outline. Ambulacral pores 

 elongated, apparently yoked. 



Mouth opening well forward, broad, two-lipped. Anus high up on the 

 truncated posterior end. 



Numerous large spines much like those of Schizaster have been found at 

 one locality in the Martinez, but if they belong to this genus at all they were 

 probably derived from another and much larger species. Tubercles larger 

 on the actinal surface. Peripetalous fasciole quite distinct on one specimen. 

 Traces of what appears to be the lateral fasciole have been seen beneath the 

 anus. 



Though crushed fragments of this species have been 

 known to the writer for some years, the first recognizable 

 specimens were discovered by the members of the class in 

 palaeontology, in April, 1897. 



Not rare in the Martinez in Contra Costa County. Spec- 

 imens preserved only as impressions or casts, usually badly 

 crushed. 



