282 



University of California Publications. 



[Geology 



row poriferous bauds, which narrow down sharply near the end 

 of the petal. In other petals poriferous bands are full width 

 almost to ends of petals. Lateral petals straight, diverging' at an 

 angle of from 105° to 130° ; interporiferous space narrower, 

 poriferous bands wider than in anterior petal. Posterior petals 

 oval, poriferous bands broad. 



Mouth opening eccentric, corresponding to vertex of test, 

 slightly sunken. Anal pore inframarginal. Ambulacral furrows 

 well marked in posterior part of aetinal surface, branching close 

 to mouth, main branches continuing almost parallel for last three- 

 fourths of their length. A second branch enters the interambu- 

 lacral areas about half way from mo.uth to margin ; many smaller 

 branches from all main ones. Three or four of the stronger 

 interambulacral furrows continue on upper surface of test to 

 the upper ends of the petals. In posterior and sometimes in lat- 

 eral petals a central furrow reaches almost to the apical system. 

 Furrows poorly marked in anterior part of aetinal surface. 



Tubercles larger on aetinal than on abactinal surface, espe- 

 cially noticeable near mouth, standing here in well defined pits. 



Occurrence: Living — Alaska to San Pedro (Cooper). Pleis- 

 tocene — San Pedro (Cooper, Arnold), San Diego, Santa Barbara 

 (Arnold), ( ?) Seven Mile Beach. Pliocene — San Fernando, (?) 

 San Diego (Cooper) ; Santa Clara Valley (Arnold). 



Though closely resembling Echinarachinus gibbsii, Echinara- 

 chinus ezcentricus is probably not descended from it, for the more 

 recent and not the older specimens of Echinarachinus ezcentricus 

 show the closer relationship to the older species. Specimens from 

 the Pleistocene of San Diego show a very low degree of eccentric- 

 ity, have very thin edges, and quite long but slightly curved pos- 

 terior petals. The same is true of all the specimens examined 

 which were referred to the Pliocene. 



ECHINABACHINUS GIBBSII Eemond. 



1863. Scutella gibbsii Eemond Cal. Acad. Sci., vol. 3, p. 13. 

 1868. Scutella gibbsii Eemond Gabb, Pal. of Calif., vol. 3, pi. 13, figs. 66 

 and 66a. 



1899. Echinarachinus gibbsii Eemond (Merriam) Proc. Calif. Acad. Sci., 



3rd ser., Geol., vol. 1, p. 169; pi. 22, fig. 7. 

 1907. Echinarachinus ashleyi (Merriam, M. S. ), Arnold, U. S. G. S. Bull. 



322, pi. 24, figs. 6 and 7. 



