118 University of California PiiMications in Geology [Vol. 12 



petals ; pores of all petals continue beyond the ends of the petals to 

 the margin. Inferior surface concave to the mouth. Peristome slightly 

 sunken and situated posterior to the center of the test, and approxi- 

 mately opposite the apex of the test. Periproct round, inframarginal, 

 and placed from one to two times its own diameter from the edge of the 

 test, the distance being greater in the larger specimens. Ambulacral 

 furrows branch dichotomously a short distance from the peristome 

 and again near the margin ; all pass over the upper surface as lines, 

 which extend toward the ajiical system. Tubercles prominent, scro- 

 bicular, small, and numerous on the interambulacral areas, but on the 

 petaliferous areas they are considerably larger and fewer in number ; 

 on the inferior surface the tubercles are large, but near the ambulacral 

 furrows become quite small and very numerous. 



Related forms. — Dendraster eoalingaensis Twitchell is closely re- 

 lated both to D. gibbsii (Remond) and D. arnoldi Twitchell. It may 

 be distinguished from the former by having a much less eccentric 

 apical system and smaller angle between the petals of the bivium ; 

 the test is relatively thicker, especially at the margin ; the petaliferous 

 areas are more tumid ; tubercles are larger and not of a uniform size 

 over the surfaces ; and the petals of the bivium are longer and nar- 

 rower; moreover, the lateral petals of D. gibbsii are in most specimens 

 flush with the surface of the test, and only in exceptional specimens 

 are they slightly elevated, but in D. coalingaensis they are usually ele- 

 vated. In D. gibbsii the upper surface is regularly arched to the 

 summit, whereas in the D. coalingaensis the profile is irregular, the test 

 being somewhat flattened in the submarginal area, and usually with a 

 lower apex. D. arnoldi Twitchell has some general similarities, yet 

 may be distinguished from D. coalingaensis by having a relatively 

 thicker test and margin and a less eccentric apical system. D. perrini 

 (Weaver) belongs to the same group as D. coalingaensis, but is easily 

 separable on account of its relatively greater thickness ; more centrally 

 located apical system, with correspondingly longer petals of the 

 bivium ; by its wider petals ; in that the posterior margin is usually 

 triuicated ; and in that the tubercles are of uniform size and compara- 

 tively smaller. 



Geologic horizon. — Upper Etchegoin formation, Middle Pliocene. 

 Associated with D. hesperis Kew and D. hesperis var. gibbosus Kew. 



Localities. — Holotype from "near A. Kreyenhagen 's place," Za- 

 pata Creek (Twitchell) ; all occur in the Coalinga district, Fresno 

 County, California; figured specimen from Univ. Calif, loc. 2108. 



