92 University of California Puhlioaiions in Geology [Vol. 12 



stome central, round, and slightly depressed. Periproct round, large, 

 and inframarginal, nearly marginal. Test covered with small tubercles 

 of nearly the same size on both surfaces which have sunken serobicules. 

 Internal structiire consists of radial partitions extending from the. 

 margin for about one-half the distance toward the center, and con- 

 tinuing as ridges on the floor to the perignathic girdle. No concentric 

 ridges appear to be present. 



Related forms. — Although Astrodapsis Tjrewerianus resembles the 

 form A. eierhoensis (Kew), it may be distinguished by the narrower 

 petals, absence of interambulacral depressions, very indistinct or no 

 ambulaeral furrows, a relatively more elevated test, and petals which 

 are never raised. 



Geologic horizon. — Briones formation, or Astrodapsis brewerianus 

 beds, which lie conformably below the San Pablo group. Upper Mio- 

 cene, and, with a probable unconformity, above the Monterey group. 

 Middle Miocene. 



Localities. — Walnut Creek, Gregory Ranch (?), Contra Costa 

 County, California (figured specimen, J. C. Merriam, 1899) ; San 

 Pablo Bay, Contra Costa County; Western Pacific R. R. cut, "Verona, 

 Pleasanton quadrangle, California (Leland Stanford Jr. Univ. Coll.). 



ASTEODAPSIS BEBWEEIANUS DIABLOENSIS Kew, n. var. 

 Plate 13, figure 6 



Holotypc.—'No. 11335 Univ. Calif. Coll. Invert. Pal. 



This variety differs from Astrodapsis ireweriamis (Remond) in 

 that the petaliferous portions of the ambulacra are elevated; that the 

 test grows to be somewhat larger, and the outline is slightly more 

 elongate. All gradations may be found between those having raised 

 petals and those having petals flush with the surface of the test. 

 These are found associated together. 



Belated forms. — It differs from Astrodapsis eierhoensis (Kew) in 

 that the petals are narrower and the margin relatively thinner. From 

 Astrodapsis tiimidus Remond it may be separated by the lack of inter- 

 ambulacral depressions, in that the ambulaeral furrows are not so 

 well developed, and the petals usually are not so highly elevated. 



Geologic horizon. — Astrodapsis brewerianus zone, Briones forma- 

 tion, Middle Miocene. Associated with Astrodapsis brewerianus 

 (Remond). 



Locality.- — One-half mile northeast of Las Trampas Peak, Contra 

 Costa County, California. Type from Univ. Calif, loc. 1191. 



