1920] Kew: Cretaceous and Cenozoic Echinoidea 



95 



margin and near the end of the petal ; outer rows at first diverge 

 slightly more than the inner rows and then converge markedly at the 

 same point, close to the inner rows ; double rows of small, rounded 

 pores extend in nearly parallel lines to the ambitus, and in some 

 specimens on the under surface as a continuation of the pores of the 

 petal proper. Interporiferous areas wade, being about three times 

 the width of each poriferous area. Odd anterior petal narrower than 

 the paired ones. Actinal side concave. Peristome central, small, and 

 subcircular in outline. Periproct small and round ; marginal to infra- 

 marginal. Ambulacral furrows not usually shown except in occasional 

 specimens, where broad indistinct grooves and bifurcating ambulacral 

 lines are present, the latter extending on the upper surface. In un- 

 weathered specimens the tubercles are small but with prominent 

 mamelons, quite numerous, and of the same size on both surfaces. 



Belated forms. — This form is closely related to Astrodapsis brew- 

 erianus (Remond). It differs in possessing broader petals, which are 

 more elevated. It may be separated from A. breivcrianus var. diablo- 

 ensis Kew in having wider petals with relatively narrower poriferous 

 areas, and in that the interambulacral areas are usually somewhat 

 depressed. From Astrodapsis tumidus Remond it may be distin- 

 guished by its wider petals, which are not so strongly elevated ; by 

 its usually broader poriferous areas and thicker margin, and in that 

 the ambitus is not so markedly notched in the ambulacral areas ; more- 

 over, the interambulacral depressions are usually absent or faint. 

 It may be easily separated from A. margaritanus Kew by its more 

 tumid test and wider petals. 



Although in a former paper this form was made a subspecies, 

 subsequent investigation has shown that it is entitled to the rank of 

 a species, for the reason that it possesses broader petals than either 

 A. tumidus or A. brcweriauus, and that, although it shows intergra- 

 dational characters, the constant characters, such as the markedly 

 swollen test, wide petals, and slightly depressed interambulacral areas, 

 distinguish it as a separate species. 



Geologic horizon. — Lower San Pablo group, in beds above the 

 Astrodapsis brewerianus zone or Briones formation and below tlie 

 Astrodapsis tumidus zone. Associated with Astrodapsis { .^) pabloensis 

 (Kew). 



Locality. — San Pablo Bay and Mount Diablo region. Cotype, 

 specimen no. 10061 from Univ. Calif, loc. 522; cotyi^e, specimen no. 

 10062 from Univ. Calif, loc. 526. 



