MIOCENE ECHINODEKMATA. 193 



The periproct is very small, circular, inframarginal, nearly marginal. 



Related forms. — D. arnoldi is closely related to D. perrini, but can be separated from it by 

 its smaller petaloidal area and broader submarginal area, its relatively shorter posterior petals, 

 its narrower interporiferous areas, and its narrower and less rapidly widening petals. D. arnoldi 

 is liable to be confused with D. coalingaensis at times, but is to be distinguished from the latter 

 by its thicker margin, less symmetrically elliptical petals wide open at the ends, its more con- 

 spicuous tubercles, and its less posteriorly excentric apex. 



Localities. — Near A. Kreyenhagen's place and south of Lucile Well, 2 miles southwest of 

 Coalinga in Coalinga district, California. 



Geologic horizon. — Etchegoin formation, upper Miocene and lower Pliocene (?). 

 * Collection.— V . S. National Museum (165707). 



Dendraster gibbsii (Remond). 

 Plato LXXXIX, figs, la-b, 2-4; Plate CVIII, B. 



Scutella gibbsii Remond, 1863, California Acad. Sci. Proc, vol. 3, pp. 13, 14. 



Scutella gibbsii Meek, 1864, Smithsonian Misc. Col., vol. 7 (183), p. 2. 



Scutella gibbsii Gabb, 1S69, Geol. Survey California, Paleontology, vol. 2, pp. 37, 109, PI. XIII, figs. 66, 66a. 



Scutella gibbsii Cooper, 1888, Cat. California fossils, State Mineralogist Seventh Rept., p. 271. 



Eckinarachnius gibbsii Merriam, 1S99, California Acad. Sci. Proc, 3d ser., Geology, vol. 1, No. 5, p. 169, PL XXII, 



fig. 7. 

 IScutella gibbsii F. Anderson, 1905, California Acad. Sci. Proc, 3d ser., Geology, vol. 2, p. ISO. 

 Eckinarachnius ashleyi (Merriam, MS), Arnold, 1907, U. S. Geol. Survey. Bull. 322, PL XXIV, figs. 6, 7. 

 "? Eckinarachnius excentricus Eschscholtz var. Arnold and Anderson, 1907, IT. S. Geol. Survey Bull. 322, PL XXIV, 



fig. 8. This is apparently a somewhat variant form of Dendraster gibbsii. 

 Eckinarachnius gibbsii Arnold, 1909 (pars), U. S. Geol. Survey Bull 396, pp. 24, 25, 27, 31, 34 (pars); 38, 42 (pars), 132, 



144, 146; PL XIII, figs. 1, 2; PL XIX, figs. 1, 2; PI. XX, fig. 7. 

 non Eckinarachnius gibbsii Arnold, 1909, (pars), U. S. Geol. Survey Bull. 396, pp. 34 (pars), 42 (pars), 162; PL XXVIII, 



figs. 4, 4a. 

 Eckinarachnius gibbsii Arnold and R. Anderson, 1910 (pars), U. S. Geol. Survey Bull. 398, pp. 316, 318; PL XLI, figs. 



1, 2; PL XLII, fig. 7. 

 non Eckinarachnius gibbsii Arnold and R. Anderson, 1910 (pars), U. S. Geol. Survey Bull. 398, p. 338; PL L, figs. 4, 4a, 

 Dendraster ashleyi Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 706. 

 Dendraster gibbsii Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 704. 



Determinative characters. — Test small to large, suboblong, subquadrate, suboval, or sub- 

 ovate in marginal outline, length usually equal to or greater than width, though sometimes 

 considerably less, usually broadest back of the center; upper surface convex, much depressed, 

 though less so posteriorly than anteriorly, rising directly from the thin margin to the low, 

 posteriorly excentric apex; undersurface flat. Apical system very excentric posteriorly, from 

 one-third to more than one-half the radius from the center. Ambulacral petals large, all but 

 the odd petal approaching rather close to the margin; the posterior pair shorter than the others, 

 more divergent than the anteriorly curving anterior pair and with widely divergent poriferous 

 zones. Peristome small, excentric posteriorly, though less so than apical system; ambulacral 

 furrows fork near the peristome, the branches at first diverging then converging slightly and 

 proceeding nearly to the margin, giving off only a few branches. Periproct very small, cir- 

 cular, inframarginal, nearly marginal. 



Dimensions. — Specimen A (PI. LXXXIX, figs, la, lb): Length 62 millimeters; width 59 

 millimeters; height 13 millimeters. Specimen B (PI. LXXXIX, fig. 2): Length 87 millimeters; 

 width SI millimeters; height 11 millimeters. Specimen C (PI. LXXXIX, fig. 3): Length 81 

 millimeters; width 95 millimeters; height 16 millimeters. Specimen D (PI. LXXXIX, fig. 4): 

 Length 32 millimeters; -width 33 millimeters; height 7 millimeters. 



Description. — A very good description of this interesting Californian species was given as 

 early as 1S63 by Remond. It was first figured by Gabb in 1S69. The test is variable in size, 

 ranging from about 1 to 3£ inches in diameter and from one-eighth to one-half inch in height. 

 In marginal outline it varies considerably, being usually suboblong or subquadrate; sometimes 



