1920] Kew: Cretaceous and Cenozoic Echinoidea 



125 



DENDRASTER HESPERIS Kew, n. sp. 

 Plate 26, figures la, Ih, Ic 



Holotype.— No. 11381 Univ. Calif. Coll. Invert. Pal. 



Test of medium size. Measurements of holotype : anteroposterior 

 diameter 47.5 mm., transverse diameter 51.4 mm., greatest height 

 12.0 mm. Marginal outline subcircular, the greatest diameter being 

 either in an anteroposterior or transverse direction ; greatest trans- 

 verse diameter immediately posterior to the center of the test. 

 Upper surface depressed and arching regiilarly to the summit, the 

 latter being slightly eccentric to the posterior. Margin rounded and 

 of moderate thickness ; truncated in the posterior interambulacral 

 area and indented by a broad notch, which continues toward the 

 apical system as a wide, shallow depression on the upper surface. 

 Apical system eccentric to the posterior, being situated about one- 

 fourth the radius of the test from the center. Madreporite large 

 and pentagonal ; four genital pores present, with the two anterior 

 ones closer together than the posterior pair ; perforated radial plates 

 are placed at the base of each petal. Ambulacra wide at the ambitus, 

 where they are broader than the interambulacra. Dorsal portions 

 petaloid. Petals slightly elevated, moderately broad, and open at their 

 extremities ; those of the bivium about two-thirds the length and 

 slightly wider than those of the trivium ; inner rows of pores of the 

 paired petals diverge and then slightly converge at their ends ; outer 

 rows diverge to a slightly greater degree and then converge so as to 

 meet the inner rows at the extremity of the petal ; anterior rows of 

 pores curve slightly more than the posterior rows, giving the petal 

 the appearance of being bent backward. Odd anterior petal symmet- 

 rical, the rows of j)ores diverging and then converging slightly to the 

 end. A few pores continue beyond to the margin in all the petals. 

 Poriferous areas of the petals of the bivium widest, each being about 

 one-half the width of the interporiferous area ; that of the anterior 

 paired petal about one-third, and that of the odd anterior one about 

 one-fourth the width of the interporiferous area. Under surface 

 slightly concave, deepening toward the center. Peristome large, situ- 

 ated slightly posterior to the center of the test. Periproct of medium 

 size, inframarginal, and distant from the margin the length of its own 

 diameter or more. Tubercles relatively prominent and irregularly 

 distributed over the test ; mamelons are present, which project above 

 rather wide scrobicules. Ambulacral furrows are well marked, divide 



