1920] 



Kew: Cretaceous and Cenozoic Echinoidea 



123 



posterior direction ; greatest width usually posterior to the center, 

 but in front of the apical system. Upper surface depressed but 

 arching regularly to the summit, which is eccentric posteriorly and 

 anterior to the apical system. Apical system situated far back, to- 

 ward the posterior edge of the test, the distance from the center of 

 the test to apical system" averaging about two-fifths the distance from 

 the center to the posterior edge. Margin rounded ; usually pos- 

 sessing a notch in the posterior interambulacral area, which continues, 

 in most specimens, as a shallow depression on the upper surface toward 

 the apical system. Madreporic body large and subpentagonal in out- 

 line ; produced posteriorly into the interambulacral area, forming a 

 small lobe ; four large genital pores at the anterior corners of the 

 madreporite, the two anterior ones being closer together than the 

 posterior ; five perforated radial plates, situated at the base of the 

 petals. Interambulacra wider than the ambulacra at the margin ; 

 dorsal portions of the ambulacra petaloid. Petals moderately broad, 

 wide open at their extremities, and reaching a point that is slightly 

 over three-fourths the distance to the margin ; usually flush with 

 the test, but the lateral petals may be somewhat raised. Lateral 

 petals unsymmetrical ; those of the bivium about one-half the length 

 of the trivium, though of the same width ; inner rows of rounded 

 pores diverge at first and then converge slightly ; pores conjugated ; 

 outer rows of elongate pores diverge to a greater degree and then 

 converge close to the inner rows at the extremity of the petal ; in the 

 anterior i^aired petals the convergence of the inner rows is less ; the 

 convergence of the anterior rows of pores in both sets of petals 

 greater than in the posterior rows ; odd anterior petal symmetrical 

 and elliptical in outline. Poriferous areas of the paired petals of the 

 same width, each being equal to about one-half the width of the inter- 

 poriferous area ; poriferous area of the odd anterior petal narrower 

 and with a correspondingly wider interporiferous area. Average 

 angle between the petals of the bivium 124 degrees. Inferior surface 

 flat or very slightly concave. Peristome small, irregular in outline, 

 and posteriorly eccentric, though to a less degree than the apical 

 system, and corresponding closely with the eccentricity of the apex. 

 Ambulacral furrows well marked ; dichtomously branched near the 

 peristome, which in turn send off numerous branches that continue 

 over the upper surface for a short distance ; odd anterior ambulacral 

 furrows are less developed than the others ; main branches send off 



