1920] Keiv: Cretaceous and Cenozoic Echinoidea 89 



subcircular in outline. Anibulacral furrows well marked, straight, 

 and continuing over the upper surface, in weathered specimens, as 

 sutural lines. Tubercles small, scrobieular, perforated, numerous, 

 and equally distributed on both surfaces of the test. 



This species shows a great variety of forms from the same locality. 

 These variations include individuals with margins varying from quite 

 thin to very thick, and from a highly elevated to a depressed test ; 

 the petals also vary in their elevation and in width. In as much 

 as gradations can be found between the extremes of the variations 

 all the forms have been included under a single subspecies. 



Related foryns. — From Astrodapsis major Kew, to which it is closely 

 allied, A. arnoldi peltoides dilfers in possessing prominent grooves in 

 the ambulacral areas along the margins of the petals ; in that the petals 

 are usually narrower, and the interambulacral depressions are in most 

 specimens not so deep. It can be distinguished from A. arnoldi 

 arnoldi (Pack) as being more strongly elliptical in marginal outline; 

 in that the actinal surface shows a greater degree of concavity, and 

 in that the petals are usually narrower. It differs from A. jacalito- 

 sensk Arnold in having deep interambulacral grooves. From A. arnoldi 

 crassus Kew it is distinguished by having a smaller peristome, and 

 usually a more elongate marginal outline; from A. arnoldi var. frcs- 

 noemis Kew, in having a more elongate outline and wider petals. 

 A. arnoldi spatiosiis Kew may be separated by its extremely wide 

 petals, greatly depressed test, and less strongly elevated petals. 



Geologic horizon. — Lower Etchegoin (Jacalitos) formation, Lower 

 Pliocene. Associated with Dendraster gibbsii (Remond). 



Localities. — Holotype from Trophon zone, at head of Zapato Chino 

 Creek, Coalinga district, Fresno County, California, Calif. Acad. Sci. 

 Coll. loc. 293. 



ASTRODAPSIS ARNOLDI SPATIOSUS, Kew, n> subsp. 

 Plate 22, figures 2a, 2h 



Holotype.— 'No. 11041 Univ. Calif. Coll. Invert. Pal. 



Test large. Measurements of holotype : anteroposterior diameter 

 75 mm., transverse diameter 69 mm., greatest height 14.5 mm. Out- 

 line siibcircular, tending to be slightly pentagonal. Margin notched 

 indistinctly in the posterior ambulacral areas and in the odd posterior 

 interambulacral area, rounded and thickened. Upper surface greatly 

 depressed, gently arching to the summit, which is anterior to the 



