MIOCENE ECHINODERMATA. 195 



Geologic horizon. — Jacalitos and Etchegoin formations, in Coalinga district, upper Miocene 

 and lower Pliocene (?). Fernando formation in Santa Maria district, upper Miocene or lower 

 Pliocene. 



Collections— U. S. National Museum (165547, A; 165611, B, C; 165704, D); University 

 of California, California Academy of Sciences; Yale University. 



Dendraster oregonensis (Clark). 



Plate XC, figure 1. 



Scutella (Echinarachnius) oregonensis Clark, 1909, in Da'U, U. S. Geol. Survey Prof. Paper 59, p. 140, PI. VII, fig. 2. 



Determinative characters. — Test small; subcircular in marginal outline, broader posteriorly 

 than anteriorly; the whole form greatly depressed, the upper surface moderately convex, 

 rising directly from the rather thin margin to the low, anteriorly excentric apex; under surface 

 flat. Apical system excentric posteriorly, about one-fourth the radius from the center. Ambu- 

 lacral petals relatively large, approaching rather close to the margin; the two posterior shorter 

 than the anterior three and with posterior poriferous zones straight or nearly so; open at their 

 ends. Peristome circular, subcentral. Ambulacral furrows feeble. Periproct small, sub- 

 circular, supramarginal. 



Dimensions. — Length 20 millimeters; width 20 millimeters; height 3 millimeters. 



Description. — This recently described Pacific coast Dendraster is one of the smallest 

 representatives of the genus, rarely exceeding an inch in diameter. 



In marginal outline it is subcircular; though broader posteriorly than anteriorly. The 

 whole form is greatly depressed, the upper surface being evenly rounded and rising directly 

 from the rather thin margin to the low apex which is situated forward of the center. The 

 under surface is flat or faintly concave. 



The ambulacral areas are rather narrow; dorsal portions petaloid. The petals are rela- 

 tively large, approaching rather close to the margin, the two posterior shorter than the anterior 

 three, of which the odd petal is the longest. The petals are straight or nearly so, the anterior 

 pair shghtly more divergent than the posterior pair, and all are open at their ends. The 

 poriferous zones are broad, pores oval, pairs of pores conjugated; the posterior zones of both 

 pairs straight or nearly so. The interporiferous areas are narrow, about as wide or shghtly 

 wider than the poriferous zones. 



The interambulacral areas are broad, about equally so between the petals. The surface 

 of the test is closely set with small tubercles, apparently imperforate, set in deep scrobicules, 

 the tubercles being slightly larger on the under surface. 



The apical system is excentric posteriorly, being situated about one-fourth the distance 

 from the center to the posterior border. The details could not be made out upon the specimens 

 studied. 



The peristome is small, circular, subcentral; the ambulacral furrows feeble, not showing 

 very well upon the specimens; but apparently simple and straight for a short distance from 

 the peristome, then forking symmetrically. 



The periproct is small, subcircular, supramarginal, about 1 millimeter from the posterior 

 ends. 



Related forms. — D. oregonensis is closely allied to D. interline aius, the superficial resemblance 

 being very striking, but differs in having all the petals open at the ends and the posterior and 

 anterior paired petals less symmetrically subelhintical in form by reason of the fact that the 

 posterior poriferous zones are straight or nearly so. D. oregonensis also differs in being relatively 

 higher in proportion to its width and has a relatively larger periproct. These differences are 

 not very pronounced, and further collecting may result in the merging of the two species. 



Localities. — Near Empire City and Fossil Point, Coos Bay, Oreg. 



Geologic horizon. — Empire formation, upper Miocene. 



Collection— U '. S. National Museum (153975). 



