1920] 



Keiv: Cretaceous and Cenozoic Echinoidea 



119 



DENDEASTEE DIEGOENSIS Kew, n. sp. 



Plate 29, figures la, 16, 2; plate 30, figures 1, 2a, 2b 



Dendraster excentricus. Clark and Twitohell, U. S. Geol. Surv. Mon., vol. 

 54, 1915, pp. 223-225, pi. 104, figs, la, lb, Ic, Id. 



HoloUjpe.—m. 12257 Univ. Calif. Coll. Invert. Pal. 



Test large. Measurements of holotype: anteroposterior diameter 

 77 mm., transverse diameter 82.5 mm., greatest height 9 nun. Mar- 

 ginal outline subcircular, with indistinct shallow notches at the ambitus 

 in the ambulacral areas. Upper surface somewhat flattened in the 

 submarginal area, and then arching within the radius of the petals 

 to the apex which may be moderately low or markedly high ; it varies 

 in position from a point slightly anterior to the center of the test to a 

 point coincident with the apical sj'stem. Apical system eccentric from 

 one-third to one-sixth the distance of tlie radius. Madreporic area 

 pentagonal in outline ; four large genital pores present in the anterior 

 corners ; five small pores in the radial plates at the base of the petals. 

 Petals of the bivium unsymmetrical, sliorter but wider than those of 

 the trivium, and tending to close but half the width of the interporif- 

 erous area; posterior inner rows of pores form a nearly straight line, 

 whereas the anterior rows are considerably curved ; of the outer rows 

 the anterior are more curved. Petals of the trivium of about the same 

 length and breadth ; interporiferous area of the lateral pair about two 

 and one-half times the width of each poriferous area. Anterior lateral 

 petals nearly symmetrical, the anterior rows of pores having a curva- 

 ture slightly greater than tlie posterior rows. Odd anterior petal sym- 

 metrical ; poriferous areas extremely nari'ow, being about one-sixth the 

 width of the interporiferous area ; both rows of pores regularly curved, 

 so that the oi:)ening at the end of the petal is about one-half the width 

 of the broadest part of the petal. Inferior surface flat. Distinct am- 

 bulacral furrows branch dichotomously almost immediately from the 

 peristome and continue to the margin of the test ; smaller subsidiary 

 lines are given off which extend over the upper surface for a considera- 

 ble distance. Peristome rather small, round, and subcentral. Periproct 

 inframarginal and situated about two to three times its own diameter 

 from the margin. Tubercles small, scrobicular, and similar over both 

 surfaces except that they become somewhat larger near the peristome. 



Related forms. — This form differs from the Recent Dendraster 

 excentricus (Eschscholtz) on account of its narrower poriferous areas 

 and wider interporiferous areas of the petals; in that the anterior 



