1920] 



Kew: Cretaceous and Cenozoic Echinoidea 



117 



DENDEASTER COALINGAENSTS Twitehell 

 Plate 28, figures la, lb, Ic 



Echinarachnius gihbsii. Arnold, in part, U. S. Geol. Surv. Bull., no. 396, 



1909, pp. 34, 42, 162, pi. 28, figs. 4, 4a. 

 (.') Astrodapsis sp. indet. Arnold. U. S. Geol. Surv. Bull., no. 396, 1909, 



p. 30, pi. 28, figs. 5, 5a. 

 Echinarachnius gibbsii. Arnold and R. Anderson, in part, U. S. Geol. Bull., 



no. 398, 1910, p. 338, pi. 50, figs. 4, 4a. 

 {?) Astrodapsis, sp. indet. Stefanini, Boll. See. geol. ital., vol. 30, 1911, 



p. 703. 



Dendraster coalingaensis Twitehell. U. S. Geol. Surv. Mon., vol. 54, 1915, 



pp. 196-197, pi. 90, figs. 2a-2c. 

 (?) Sismondia coalingaensis Twitehell. U. S. Geol. Surv. Mon., vol. 54, 



1915, p. 183, pi. 85, figs. 2a, 2b, 2c. 



Holotype. — No. 165537 U. S. Nat. Mus. ; figured specimen, no. 

 11383 Univ. Calif. Coll. Invert. Pal. 



Test of medium size. Average measurements : anteroposterior di- 

 ameter 32.1 mm., transverse diameter 34.2 mm., greatest height 7 mm. 

 Outline usually subcircular, but in some specimens longitudinally or 

 transversely suboval, the greatest transverse diameter being anterior 

 to the center of the test. Upper surface greatly depressed, especially 

 in the submarginal area ; the adult specimens have a relatively greater 

 elevation than the younger ones. Summit situated posterior to the 

 center of the test, but anterior to the apical system. Margin slightly 

 thickened. Apical system quite eccentric to the posterior, the distance 

 from the apical system to the posterior margin in most specimens being 

 equal to about two-tifths of the anteroposterior diameter of the test. 

 Four genital pores are present. Madreporic area comparatively small. 

 Ambulacra wide, being widest at the margin, where they are nearly 

 twice the width of the interambulacra. Petaliferous area relatively 

 long and extending about two-thirds the distance from the apical sys- 

 tem to the margin ; those of the trivium longer than those of the 

 bivium, with the odd anterior one longer than the anterolateral pair. 

 Angle formed between the petals of the bivium is considerably greater 

 than the angles between the other petals. Lateral petals bent slightly 

 backward. Interporiferous areas of the lateral petals usually some- 

 what tumid, whereas that of the odd anterior one is nearly flush with 

 the surface of the test. Rows of pores tending to close but little at the 

 extremities of the petals ; poriferous areas relatively narrow, each being 

 about one-third the width of the interporiferous area ; poriferous areas 

 of the odd anterior petal somewhat narrower than those of the lateral 



