1920] 



Ketv: Cretaceous and Cenozoic EcMnoidea 



109 



Neotype (Merriam).— No. 11329 Univ. Calif. Coll. Invert. Pal.; 

 figured specimens, nos. 11006, 11008, Univ. Calif. Coll. Invert. Pal. 



Test small. Average measurements: anteroposterior diameter 36.5 

 mm., transverse diameter 30.4 mm., greatest thickness 8.8 mm. Test 

 depressed, subcireular to suboval in outline. Margin tumid and dis- 

 tinctly notched at the ambitus in the ambulacra, tlie notching being 

 deeper in the two posterior areas. Superior surface usually regularly 

 arched to the summit, but in some specimens the submarginal area is 

 slightly flattened. Apex coincides with, or is immediately anterior 

 to the apical system. The majority of specimens have a marked depres- 

 sion or median groove in the interambulacral areas which extends from 

 the margin to the summit. Apical system central ; madreporic area 

 pentagonal, with four genital pores present, the one opposite to the 

 posterior interambulacral area being absent. Petals prominently 

 elevated and extending, wide open, to the edge of the test. Pores 

 conjugate ; inner rows of rounded pores only slightly converge near 

 the margin, whereas the outer rows of elongate pores distinctly con- 

 verge ; when about three-fourths the distance to the ambitus, the two 

 rows of pores beconae rounded and continue in parallel lines to the 

 margin. Interporiferous areas wide, being about four times the width 

 of the poriferous areas ; odd anterior petal is slightly narrower and 

 less constricted than the otlicrs. Inferior surface more or less con- 

 cave to the peristome. Mouth sunken, central, large, and subpentag- 

 onal in outline. Ambulacral furrows distinct, broad, branching a 

 little over half the distance to the margin, and extending through the 

 marginal notches to the upper surface, where the main furrows form 

 indistinct median grooves on the petals ; suture lines between the inter- 

 ambulacral and ambulacral plates are formed by the extension of the 

 branching ambulacral lines. Periproct large, round, and situated close 

 to the margin on the under surface. Tuberculation distinct; tubercles 

 scrobicular, of medium size, and similar on both surfaces except that 

 they are somewhat smaller in the depressions of the superior surface. 

 Internal skeleton consists of strong, radially placed partitions in each 

 ambulacral area, which reach to the roof for about one-fourth the 

 distance from tlie ambitus to the peristome, and continue to the mouth 

 as low ridges on tlie floor of the test ; a few concentric ridges are 

 present near the edge of the test, connecting the radial partitions ; 

 remainder of the floor more or less roughened. 



