104 University of California Publications in Geology [Vol. 12 



mm., transverse diameter 36.8 mm., greatest height 7.5 mm. Outline 

 of test oval to subpentagonal, the greatest diameter being in the an- 

 teroposterior direction ; margin relatively thin ; upper surface greatly 

 depressed, nearly flat, but rising gently to a low apex situated on the 

 odd anterior petal immediately in front of the apical system ; inter- 

 ambulacral areas sunken into broad indistinct grooves. Marginal 

 notches in the ambulacral areas are usually present, the notches being 

 deeper in the two posterior areas. Apical system central. Ambu- 

 lacral areas wider, being one and a-half times the width of the inter- 

 ambulacral areas at the margin. Petals symmetrical ; inner rows of 

 pores diverging gradually nearly to the margin ; outer rows diverging 

 and then slightly converging until they almost merge with the inner 

 rows close to the edge of the test. Odd anterior petal narrower than 

 the others, with the anterior pair slightly wider than the posterior two. 

 Interporiferous area very wide, being about four times the width of 

 each poriferous area. Petals ])rominently elevated. Lower surface 

 concave to the peristome, which is central. Ambulacral furrows, 

 broad, deep, extending to the margin, and continuing as faint lines 

 through the notches on the upper surface as median lines on the 

 petals for about one-half the distance to the apical system. Tubercles 

 on the upper surface of moderate size, scrobicular, numerous, and 

 slightly smaller in the depressed regions of the interambulacral areas. 

 Periproct small, round, and situated close to the margin on the inferior 

 surface. 



Related forms. — This form belongs to the Astrodapsis antiselli 

 Conrad group, and appears to represent a stage of evolutionary devel- 

 opment equivalent to that of Astrodapsis cierboensis (Kew) from the 

 Lower San Pablo group. It differs in having narrower petals ; a thin- 

 ner test ; in that it possesses interambulacral grooves ; and in that it 

 attains a greater size. Its most distinctive character lies in the fact 

 that it has a remarkably flat test, with distinctly raised petals. It 

 differs further from A. antiselli Conrad by the smaller size of its 

 tubercles and in its greatly depressed test. 



Geologic horizon. — Upper San Pablo group (Santa Margarita for- 

 mation), LTpper Miocene. Associated with Astrodapsis tumidus 

 Eemond and A. whitneyi Remond. 



Localities. — Cotypes from type locality for the "Santa Margarita" 

 (San Pablo) formation, near the town of Santa Margarita, San Luis 

 Obispo County, California, Univ. Calif. Iocs. 1697 and 1707. Mouth 

 of Swain's Canyon north of Bradley, Monterey County, California 

 (U. S. Geol. Surv. ColL). 



