1 66 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Genus Clypeaster Lamarck. 



Clypeaster (?) Brewerianus Reniond. 

 Plate XXI, Fig. 2. 



Echniarachnius Brewerianus Remond., Proc. Cal. Acad. Sci., Vol. Ill, 

 1863-67, p. 53. 



Eckinarachnius Brewerianus. Figured by Gabb., Geol. Surv. Cal., Palae- 

 ontology, Vol. II, 1869, p. 36., PI. XII, figs. 65 and 65a. 



Small forms averaging between 25 and 30 mm. in long diameter, the larg- 

 est specimen measuring about 35 mm. long. Test elliptical to circular, 

 depressed, not markedly thin at the margins. 



Ambulacra not standing in relief, broad, wide open at the ends, pores con- 

 tinuing to the margin. Inner row of rounded pores diverging gradually to 

 the margin, drawing together only very slightly at about two-thirds of the 

 distance. The outer pore rows at first diverge strongly but draw together 

 again sharply at the point where the inner rows tend to converge. At this 

 point they change their form from elongated to rounded and continue to the 

 margin nearly parallel with the inner rows. The plates of the ambulacral 

 areas increase slowly in size from the apical shield to the margin, the increase 

 being most rapid at the point where the pore rows draw together. Near the 

 margins the pores stand about half-way between the inner and outer ends of 

 the plates. 



Anus marginal to inframarginal. Tubercles nearly the same size on the 

 upper and lower sides of the test. 



Very few specimens have been obtained which show the 

 lower surface, and the writer has been unable to determine 

 the character of the ambulacral furrows. As this species 

 is closely related to Astrodapsis tumidus, in which the fur- 

 rows are clypeastroid, it is probable that they are much the 

 same here and that the Brewerianus should be classed with, 

 or near, Clypeaster rather than with EchinaracJuiius, as 

 heretofore. 



Common in the Contra Costa County Miocene. 



Genus Astrodapsis Conrad. 



Astrodapsis tumidus Remond. 

 Plate XXI, Fig. 3. 



Astrodapsis tumidus Remond., Proc. Cal. Acad. Sci., Vol. Ill, 1863-67, 



p. 52. 

 Astrodapsis tumidus. Figured by Gabb., Geol. Surv. Cal, Palaeontology, 



Vol. II, 1869, p. 37, PI. XIII, figs. 68 and 68a. 



