210 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Clypeaster? breweriantjs (Remond). 



Plate XCVI, figures 2a-c, 3. 



Echinarachnius brewerianus Remond, 1863, California Acad. Sci. Proc, vol. 3, p. 53; no figure. 



Echinarachnius brewerianus Meek, 1864, Smithsonian Misc. Coll., vol. 7 (183), p. 2. 



Echinarachnius brewerianus Gabb, 1869, Geol. Survey California, Paleontology, vol. 2, pp. 36, 109, PL XII, fig. 65, 65a. 



JSchinarachnius brewerianus Cooper, 1888, Cat. California fossils: State Mineralogist Seventh Rept., p. 271. 



Clypeaster (?) brewerianus Merriam, 1899, California Acad. Sci. Proc, 3d ser., Geology, vol. 1, No. 5, p. 166, PI. XXI, 



fig. 2. 

 Astrodapsis brewerianus Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 702. 



Determinative characters. — Test small, subelliptical to subcircular in marginal outline, 

 faintly notched opposite posterior petals, longer than broad. The whole form is much depressed; 

 upper surface somewhat convex, flattened near center, margin rather thick, rounded; apex 

 central; under surface flat near margin, slightly concave near center. Ambulacral petals sub- 

 equal, plates long and narrow, poriferous zones diverging from apical region to near margin, 

 with a slight constriction about two-thirds the way. Apical system central. Peristome 

 probably central. Periproct very small, subcircular, inframarginal, almost marginal. 

 1 Dimensions. — Specimen A: Length 32 millimeters; width 28 millimeters; height 9 milli- 

 meters. Specimen B; length 36 millimeters; width 31 millimeters; height 12 millimeters. 



Description. — This species was described but not figured by Remond as early as 1863, was 

 first figured by Gabb in 1869; and was redescribed and refigured by Merriam in 1899. The 

 test is small, rarely exceeding 1J inches in length. In marginal outline it is subelliptical to 

 subcircular, faintly notched opposite posterior petals, longer than broad. The whole form is 

 considerably depressed; the upper surface rising in gentle convex curves from the moderately 

 thick, rounded margin to a flattened area near the centrally located apex; the under surface 

 flat near the margin, slightly concave toward the center. 



. The ambulacral areas are wide, wider throughout than the interambulacral areas, the 

 plates being long and narrow in the petaloid region and just at the margin; the dorsal portions 

 petaloid. The petals are subequal in length, sharply pointed near the apical system, widening 

 rapidly for two-thirds their length, then narrowing slightly and again widening rapidly to their 

 ends where they are wide open. Several pairs of pores continue beyond the petals proper, 

 diverging from the ends of the petals to the margin. The interporiferous areas are very wide, 

 from three to four times as wide as the poriferous zones, flush or slightly tumid; poriferous 

 zones very narrow near apical system, rather wide near ends of petals; pores oval, pairs 

 conjugated. 



The interambulacral areas are relatively narrow, very narrow near the apical system. 

 The test is covered with small,, nearly uniform tubercles, which are of nearly the same size on 

 the upper and lower surfaces. 



The apical system is central and coincident with the apex. The details can rarely be 

 made out on the specimens. 



The peristome and ambulacral grooves could not be clearly made out on the specimens 

 studied. One fragment examined indicated that the peristome is small, central, or subcentral 

 and circular. 



The periproct is very small, subcircular, and inframarginal, almost marginaL 



Related forms. — This species does not appear to be closely related to any other American 

 species. It resembles Astrodapsis tumidus somewhat, as noted by Merriam, but lacks the 

 alternating tumid petals and depressed interambulacral areas characteristic of that species. 

 Until specimens showing the ambulacral grooves are found the generic position can not be 

 determined with certainty. 



Localities. — Near Lafayette, Concord quadrangle; 2 miles east of Walnut Creek House, 

 Walnut Creek, Cal. 



Geologic Tiorizon. — "Upper Contra Costa Miocene," probably San Pablo formation, upper 

 Miocene. 



Collections. — University of California (19423, B); Academy of Natural Sciences of Philadel- 

 phia (1088, A). 



