202 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



of the ambulacral ridges nearly to the apex; two faintly defined processes are given off about 

 halfway from peristome to margin, which extend to and over the margin and on the upper 

 surface between the tops of the ridges and bottom of the depressions. 



The periproct is very small, subcircular, inframarginal, almost marginal. 



Related forms. — As the location of the type is unknown, some doubt exists as to the exact 

 form which should be called A. whitneyi. The species described under the name of A. arnoldi 

 (p. 199) agrees with Remond's description of A. whitneyi as well as if not slightly better 

 than that described and figured by Merriam as A. whitneyi, which is here adopted. However, 

 Gabb figured as A. whitneyi a specimen similar to the present form, and the writer here follows 

 Merriam in regarding it as probably similar to Remond's original form. A. whitneyi is most 

 closely related to A. arnoldi, which differs in having the arch of the upper surface commence 

 nearly halfway in from the margin to the center, in having a markedly thin margin and submar- 

 ginal area, and the outer half of each petal greatly depressed and merging with the submarginal 

 area. A. whitneyi is also closely related to A. jacalitosensis, which differs in much the same way 

 as A. arnoldi, and further in having a more deeply depressed apical system, the interambulacral 

 depressions extending to and joining the apical depression, and the inner line of pores of the 

 petals diverging. A. whitneyi is also allied to A. tumidus, which is smaller, has a thicker margin, 

 and a less definitely broadly, subcorneal upper surface. 



Localities. — Kirkers Pass, north of Mount Diablo, and south shore of San Pablo Bay, Cal. 



Geologic horizon. — San Pablo formation (upper part) , upper Miocene. 



Collection. — University of California (19426). 



Asteodapsis tumidus Remond. 



Plate XCV, figures 3a-b; Plate CVIII, A. 



Astrodapsis tumidus Remond, 1863, California Acad. Nat. Sci. Proc., vol. 3, pp. 52, 53; no figure. 



Astrodapsis tumidus Meek, 1864, Smithsonian Misc. Coll., vol. 7 (183), p. 2. 



Astrodapsis tumidus Gabb, 1869, California Geol. Survey Kept., Paleontology, vol. 2, pp. 37, 110, PL XIII, figs. 68, 68a. 



Astrodapsis tumidus Cooper, 1888, State Mineralogist of California Seventh Rept., p. 270. 



Astrodapsis tumidus Merriam, 1899, California Acad. Sci. Proc, 3d ser., vol. 1, No. 5, p. 166, PI. XXI, fig. 3. 



Astrodapsis tumidus Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 703. 



Determinative characters. — Test small, circular to oval in marginal outline; margin thick, 

 especially opposite petals, faintly notched opposite petals. Whole form greatly depressed; 

 upper surface slightly and more or less regularly convex from edge to edge, with high, moder- 

 ately wide ambulacral ridges alternating with rather narrow interambulacral depressions. The 

 ridges are conspicuous for two-thirds the way from center to margin, then become nearly flush 

 with the adjacent surfaces; the depressions extend down the middle of the interambulacral 

 areas from apex to margin, widening between the petals. Apex low, subcentral; under surface 

 slightly concave. Petals wide in proportion to length, subelliptical, nearly reaching the margin; 

 poriferous zones about one-third width of tumid interporiferous areas, inner row of pores ele- 

 vated, outer row depressed. Apical system subcentral, slightly depressed below tops of petals. 

 Peristome small, circular, subcentral; main ambulacral grooves simple, straight, and deep to 

 margin, continuing over margin and nearly to apex as a faint line. Periproct very small, cir- 

 cular, inframarginal, almost marginal. 



Dimensions. — Length 30 millimeters; width 30 millimeters; height 8 millimeters. 



Description. — This species is one of the earliest reported Pacific coast fossil echinoids, having 

 been described, but not figured, by Remond in 1S63. The test is small, rarely exceeding 1£ 

 inches in diameter. In marginal outline it is somewhat variable, though usually oval or circu- 

 lar; margin moderately thick and rounded, quite thick opposite the ends of the petals, where 

 equal to more than half the height of the test, with faint notches opposite the ends of the petals. 

 The whole form is greatly depressed; the upper surface slightly and more or less regularly convex 

 from edge to edge, with high, moderately wide ambulacral ridges, which are conspicuous for 

 two-thirds of the way from the center, alternating with rather narrow, deep, interambulacral 

 depressions. The apex islow, subcentral; under surface slightly concave. 



