1920] 



Kexv: Cretaceous and Cenozoic Echinoidea 



127 



tagonal, with transverse diameter about the same length as the antero- 

 posterior diameter ; ambitus broadly but distinctly notclied in the pos- 

 terior ambulacral areas. Apex rather high, and slightly eccentric to 

 the posterior ; the greatest elevation of the test is within the area 

 limited by the length of the petals. Apical system situated immediately 

 back of the apex and center of test. Madreporic body comparatively 

 small ; a genital pore in each corner of the madreporite, except 

 the odd posterior one ; the anterior pair closer together than the 

 posterior pair. Dorsal portions of the ambulacra petaloid. Petals 

 subelliptical in outline ; rows of pores in all petals converge slightly 

 near their extremities ; petals unequal in length, those of the trivium 

 longer than the bivium, with the odd anterior one longest ; those of the 

 bivium reach a little over one-half the distance to the margin, whereas 

 those of the trivium extend about two-thirds the distance ; poriferous 

 areas narrow in comparison with the width of the petal, each being 

 about one-third the width of the interporiferous area except in the odd 

 anterior petal, where the poriferous area is about one-fourth the width ; 

 lateral petals have the poriferous areas slightly depressed ; pores con- 

 jugate and oval in shape. Inferior surface very slightly concave near 

 the peristome. Peristome small and situated but a short distance 

 posterior to the center, being approximately opposite the apex of the 

 test. Ambulacral furrows well marked, dichotomously divided a short 

 distance from the peristome, which in turn branch again before reach- 

 ing the margin. Periproct small, round, inframarginal, and situated 

 a distance about equal to its own diameter from the edge of the test. 

 Both surfaces covered by numerous small tubei'cles of uniform size. 



Related forms. — This species most closely resembles Dendraster 

 diegoensis diegoensis Kew, though differing in that the apical system 

 is slightly less eccentric ; that the peristome is more nearly central ; 

 and in that the poriferous areas of the petals are relatively narrower 

 with a complementary broader interporiferous area. In the shape 

 of its odd anterior petal it seems to be closely allied to D. ashleyi 

 (Arnold), but is easily separated on account of its less eccentric apical 

 system. From D. gibbsii (Remond) it differs in its thicker test, and 

 from D. gibbsii var. hmnilis Kew in having also a wider odd anterior 

 petal. 



Geologic horizon. — Upper Etchegoin formation. Upper Pliocene ; 

 associated with Dendraster gibbsii var. hnmilis Kew. 



Locality. — Ilolotype from Coalinga district, Fresno County, Cali- 

 fornia, Univ. Calif, loc. 2954. 



