1920] 



Kew: Cretaceous and Cenozoic EcMnoidea 



55 



Inasmuch as no material has been available for study the descrip- 

 tion used by Tvvitchell is given : 



This species, which Arnold has referred to under the name Cidaris sp. a, is 

 regarded by H. L. Clark as probably C. thouarsii. He says in a letter quoted 

 by Arnold: The wax cast {Cidari.i sp. a) is a spine of a true cidaris and very 

 much like many spines of some individuals of the species of Cidaris common on 

 the west coast of Lower California, Mexico and Central America, C. thouarsii. 

 I do not think it shows a single feature by which it can be distinguished from 

 thouarsii; it is certainly from the ancestor of that species. 



Geologic horizon. — Monterey shale, Middle Miocene. 

 Locality. — Santa Cruz quadrangle, California. 



CIDAEIS sp. a Dickerson 



Cidaris sp. a Dickerson. Univ. Calif. Publ., Bull. Dept. Geol., vol. 8, 1914, 

 p. 121, pi. 6, figs. 4«, 46. 



Cotypes.—Nos. 11729 and 11853 Univ. Calif. Coll. Invert. Pal. 

 Dickerson 's description is as follows: 



Test unknown. Spines long, very slender, circvilar in cross section. Certain 

 incomplete specimens are 15 mm. long and only 1 mm. in diameter with only a 

 slight taper. Surface of spine marked by microscopic longitudinal lines or 

 ribs. The distal end is marked by a small ball which is decorated by about 

 fourteen strong rounded ribs. This ball terminates in a rounde<l tip. The base 

 is marked by a well-developed collar and a rounded socket in its end. The 

 base does not appear to be ornamented. 



The surface of the rock is covered with spines which have been weathered 

 out. The description is based upon several fragments of spines. 



Geologic horizon. — Martinez group, Lower Eocene. 



Localities. — Mount Diablo region, Univ. Calif. Iocs. 245 and 1556. 



CIDAEIS indet. sp. 

 Cidaris sp. Kew, Univ. Calif. Publ, Bull. Dept. Geol., vol. 8, 1914, p. 51. 



Genital plates pentagonal, with rounded sides. Genital pores large. 

 Abactinal surface has a single row of primary tubercles at both mar- 

 gins of the interambulacral area. Interporiferous area contains a 

 double row of primaries. Below the ambitus tubercles sporadically 

 placed. Ambulacral area about one-third that of the interambulacral 

 area. Ambulacral pores arranged in straight radial rows. Spines 

 cylindrical, elongate, and granulated, the granulation being arranged 

 in vertical rows. Internal structure of the spines consists of rows of 

 mesh-like cells radiating from a central point. 



Specimen.— No. 12361 Univ. Calif.' Coll. Invert. Pal. 



