1920] Kew: Cretaceous and Cenozoic Echinoidea 113 



Genus DENDRASTER Agassiz 



Dendraster L. Agassiz. Catalogue Eaisonne des Eehinides; Ann. de des 



sci. nat., ser. 3, vol. 7, 1847, p. 135. 

 Echinarachnius A. Agassiz (subgenus), in part, Kevision of the Echini, 



Mus. Comp. Zool. Illus. Cat., no. 7, pt. 1, 1872, pp. 107, 315, 524. 

 Echwarachiiius. Dunean (subgenus), in part, Eevision of the genera and 



great groups of Echinoidea; Proe. Linn. Soc. London, vol. 28, 1891, 



p. 158. 



EcMnarachni'Us. Grabau and Shinier, North American index fossils, 1910, 

 p. 592. 



Dendraster. Clark and Twitchell, emend., Mesozoic and Cenozoic Echino- 

 dermata of the United States, U. S. Geo!. Surv. Mon., vol. 54, 1915, 

 p. 190. 



The genus Dendraster is used here as Agassiz originally defined it. 

 His description, translated from the French, is as follows : 



Form subcircular, depressed. Ambulacral star eccentric to the posterior. 

 Petals rounileil and unequal; the odd one longer than the anterior ambulacral 

 pair. Ambulacral furrows of the inferior surface very ramified, encroaching 

 even on to the upper surface. Anus infraniarginal as in the scutellas. Pour 

 genital pores. Differing from the scutellas by its eccentric ambulacral star. 



DENDRASTER ARNOLDI Twitchell 

 Plate 28, figures 2a, 2b, 2c 



Astrodapsis ? sp. a Arnold. U. S. Geol. Surv. Bull., no. 396, 1909, p. 162, 

 pi. 28, figs. 3, 3a. 



Astrodapsis ? sp. a. Arnold and E. Anderson, U. S. Geol. Surv. Bull., no. 



398, 1910, p. 338, pi. 50, figs. 3, 3a. 

 Dendraster arnoldi Twitchell. U. S. Geol. Surv. Mon., vol. 54, 1915, pp. 



192-193, pi. 88, figs. 4a, 4b, 4c, id. 



Holatype. — No. 165707 U. S. Nat. Mus. ; figured specimens, no. 

 165701 U. S. Nat. Mus. and 11384 Univ. Calif. Coll. Invert. Pal. 



Test small. Average measurements: anteroposterior diameter 28.7 

 mm., transverse diameter 28.1 mm., greatest height 7.2 mm. Outline 

 subcircular, with its greatest lateral diameter slightly posterior to the 

 center ; very slightly notched in the ambulacral areas. Test moder- 

 ately thickened, but much depressed ; margin thick and with upper 

 surface regularly arched to the summit, the latter being anterior to 

 the center and to the apical system. Superior surface possesses faint 

 interambulacral grooves, which may or may not be present in all 

 specimens. Apical system slightly eccentric to the posterior of the 



