1920] Ketv: Cretaceoxis mid Cenozoic Echinoidea 



153 



SGHIZASTEE MAETINEZENSIS Kew, n. sp. 

 Plate 42, figures 2a, 2b, 2c, 2d 



Holotypc—No. 11342 Univ. Calif. Coll. Invert. Pal. 



Test large. Measurements of holotype : anteroposterior diameter 

 40.9 mm., transverse diameter 32.3 mm., greatest height 21.5 mm. 

 Marginal outline subelliptical, slightly truncated in the posterior inter- 

 ambulacral area ; test moderately inflated, much less in front than 

 behind. Apical system situated about one-third the distance from 

 the center of the test to the posterior margin. Upper surface rises 

 gradually from the margin to the apex, which is placed behind the 

 apical system on a rather low, broad ridge, extending in the odd inter- 

 ambulaeral area from the apical system to the posterior margin. 

 Petals of bivium less than one-third the length of the anterior pair ; 

 anterior rows of pores in lateral petals of the trivium converge much 

 more than the posterior rows, nearly closing at the ends of the petals. 

 Odd anterior petal longer than the others, much broader, and with 

 pores rounded instead of oval in outline ; poriferous areas about as 

 broad as the interporiferous area at their widest part. Lateral petals 

 placed in narrow grooves ; the poriferous areas situated on the sides 

 of the groove, giving the petals the appearance of being quite narrow ; 

 odd anterior petal in a broad, deep groove, which narrows near the 

 margin and passes through a shallow marginal notch to the mouth 

 on the under side. Inferior surface very slightly convex, with actinal 

 plastron well developed. Peristome semicircular and sunken, with a 

 prominent posterior labrum. Periproet small, and situated high up 

 on the posterior truncation of the test. Tuberculation of the upper 

 surface not preserved ; tubercles of lower surface small, and not 

 numerous ; more crowded on the actinal plastron, but smaller toward 

 the posterior end. 



Related: forms. — This form is closely related to Scltizaster lecontei 

 Merriam, but it differs from the latter in having a more eccentric 

 apical system, longer anterolateral petals with shorter ones in the 

 bivium, and in having much narrower grooves in which the paired 

 petals are situated. 



Geologic horizon. — Martinez group. Lower Eocene ; associated 

 with Schizaster coretiformis Kew. 



Localities. — Holotype from Swett's Ranch, on coral reef, south of 

 Martinez, Contra Costa County, California, Univ. Calif, loe. 241. 



