1920] 



Kew: Cretaceous and Cenozoic Echinoidea 



133 



Holotype. — No. 153975 U. S. Nat. Mus. Figured specimens, nos. 

 449 and 450 Calif. Acad. Sci. Coll. Pal. 



Test small. Measurements of specimen no. 449 : anteroposterior 

 diameter 25.4 mm., transverse diameter 26.5 mm., greatest height 

 2.3 mm. Outline subpentagonal to subeircular. Upper surface con- 

 siderably depressed and arching to the sunnnit, which is slightly an- 

 terior to the apical system ; submarginal area somewhat flattened ; 

 margin thin. Apical sj'stem distinctly eccentric to the i^osterior. The 

 ambulacra wider than the interambulacra at the anibitus, the plates 

 of the former becoming greatly enlarged beyond the extremities of 

 the petals. Dorsal portions of the ambulacra petaloid. Petals large, 

 subelliptical in shape, asymmetric, and extending about four-fifths 

 the distance to the margin ; petals of the bivium shorter than the 

 lateral petals of the trivium, with the odd anterior one longer than 

 the others. Rows of pores of the lateral petals nearly closing at their 

 extremities; posterior inner rows in bivium and anterolateral pair 

 nearly straight ; anterior rows much curved. Poriferous area of the 

 bivium wide, each being of about the same width as the interporiferous 

 area; that of the lateral petals of the trivium not so wide, each 

 being slightly more than half the width of the interporiferous area. 

 Odd anterior petal wider than the others; poriferous area quite 

 narrow, with a correspondingly large interporiferous area, and the 

 rows of pores not converging so closely at their ends as in the other 

 petals. A few pores continue beyond the extremities of the petals. 

 Inferior surface flat except near the peristome, where it becomes 

 faintly concave. Ambulacral furrows well marked, branching about 

 one-third the distance from the peristome to the margin, with the 

 latter again branching near the edge of the test; the main furrows 

 die out when about two-thirds the distance to the margin. Peristome 

 slightly eccentric posteriorly, round in outline, and of moderate size. 

 Periproct supramarginal, and situated from the edge of the test a 

 distance equal to the width of a marginal plate. Tubercles small, 

 crowded, of the same size on the upper surface and near the margin 

 on the under surface, but become larger, more noticeably scrobiculate, 

 and le.ss crowded toward the peristome. The internal skeleton consists 

 of radiating partitions in the interambulacral areas, which connect 

 wath the upper surface near the margin, and from that place to the 

 peristome extend as thick ridges on the floor ; between these are inter- 

 communicating pillars and irregularities on the lower surface. The 

 auricles are well developed. 



