1920] 



Kew: Cretaceous and Cenozoic Echinoidea 



145 



of the trivium, whereas the odd anterior one is slightly longer than the 

 latter two. Poriferous areas large, each area being slightly wider 

 than the interporiferous area. Petals symmetrical ; inner rows of 

 pores on the lateral petals extend in straight lines to the extremity 

 of the petal, whereas the outer rows diverge markedly from the apical 

 system, and then converge close to the inner rows at the end of the 

 petal, making with the inner row a nearly perfect chord. Rows of 

 pores of odd anterior petal continue in gradually divergent lines to 

 the end, giving the petal a flaring appearance ; lateral petals wider. 

 All the petals are placed in shallow sulci, that of the odd anterior 

 petal sunken to a less degree than the others. Under surface nearly 

 flat with the exception of a large, broad, rounded keel which is pro- 

 duced posteriorly to the truncated portion of the test. Peristome 

 small, suboval, and placed well toward the front ; slightly sunken 

 and with a prominent posterior labrum. Periproct small and situated 

 high up on the truncated portion of the test. 



Related forms. — This form may be easily distinguished from 

 Epiaster depressus Kew by its much greater thickness, its very promi- 

 nent keel on the actinal surface, and much wider petals. From 

 Hemiaster cholaniensis Kew it differs in having much broader petals, 

 shallower petaliferous sulci, and the prominent actinal keel. 



Geologic horizon.- — Chico formation, Upper Cretaceous. 



Locality. — Shepherd Canyon, Contra Costa Hills, Alameda County, 

 California. 



HEMIASTEE CALIFOENICUS W. B. Clark 

 Plate 40, figures 4a, 4&, 4c 



Kemiaster calif ornicus Clark. Johns Hopkins University Circ, vol. 10, 



no. 87, 1891, p. 77. 

 Hemiaster calif ornicus Clark. Ibid., vol. 12, no. 10.3, 1893, p. 52. 

 Hemiaster calif ornicus Clark. U. S. Geol. Surv. Bull., no. 97, 1893, 



p. 90, pi. 49, figs, la, lb, Ic. 

 Hemiaster calif ornicus. Clark and Twitchell, U. S. Geol. Surv. Mon., vol. 



54, 1915, p. 96, pi. 50, figs, la, Ih, Ic, Id. 



Holotype. — No. 31203 U. S. Nat. Mus. Figured specimen, no. 

 11013 Univ. Calif. Coll. Invert. Pal. 



An echinoid of medium size. Measurements of specimen no. 11013 : 

 anteroposterior diameter approximately 28.5 mm., transverse diameter 

 28.2 mm., greatest thickness 15 mm. Outline from above subhexagonal 



