30 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



Class ECHINOIDEA. 



Subclass REGULARIA ENDOBRANCHIATA. 



Order CIDAROIDEA. 



Family CIDARID^E. 



Genus CIDARIS Leske. 

 ClDARIS CALIFORNICUS Clark. 



Plate IV, figures la-c. 



Cidaris californicus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Cidaris californicus Clark, 1893, U. S. Geol. Survey Bull. 97, p. 36, PI. VI, figs. la-b. 



Determinative characters. — Test unknown. Spines large, club-shaped, with rows of large 

 granules that coalesce to form longitudinal ridges which extend from neck to point of spine. 



Dimensions. — Largest spine: Length 22 millimeters; breadth in thickest part 5 millimeters. 



Description. — This species is based on detached spines, four or five specimens of which are 

 found in material from Taylorsville, Cal. They are distinctive in every way and can not be 

 mistaken, even in fragments. The specimens examined are casts but are so well preserved that 

 impressions in gutta-percha, from which the drawings were made, show the characters com- 

 pletely. Each spine has a short narrow neck, beyond which it rapidly increases in size so as to 

 give a club-shaped outline to the middle and upper portions. Rows of longitudinal granules 

 cover the surface from the neck to the point of the spine, presenting the appearance of long 

 serrated ridges. 



Related forms. — Separated from G. taylorensis by its club-shaped form and surface char- 

 acters. 



Locality. — Taylorsville, Plumas County, Cal. 



Geologic horizon. — Mormon sandstone, Middle Jurassic. 



Collection. — U. S. National Museum (30184). 



Cidaris taylorensis Clark. 



Plate IV, figures 2a-b. 



Cidaris taylorensis Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Cidaris taylorensis Clark, 1893, U. S. Geol. Survey Bull. 97, p. 35, PI. VI, figs. 2a-b. 



Determinative characters. — Test small. Interambulacra wide. Tubercles large, with cir- 

 cular areolas, much depressed marginally; boss crenulated; mamelon perforated. Miliary 

 space narrow. Spines long, cylindrical, covered with small granules arranged in longitudinal 

 rows. 



Dimensions. — Test small but undetermined. Largest spine: Length 30 millimeters (?); 

 width in broadest portion 5 millimeters. 



Description. — The fragments of this form, although they permit determination of but few of 

 the important characters, warrant specific description from the fact that they are totally distinct 

 from the only other representative of Cidaris from the Jurassic rocks of America. The small 

 fragments of the inter ambulacrum and the spine occur together and doubtless formed part 

 of the same individual. The interambulacral plates, of which only portions are preserved 

 on the specimen figured, indicate a form of no great size. The tubercles are large, with depressed 

 areolas surrounded by a circle of large granules. The boss is crenulated and the mamelon per- 

 forated. The miliary space is apparently narrow, the tubercles of adjacent plates in the same 

 column being nearly confluent. 



The spine is long, gently tapering toward the base in the portion preserved, and covered 

 with longitudinal rows of small granules. 



Related forms. — As the Jurassic strata of North America afford few fossil Echinodermata as 

 compared with the Cretaceous, there are not many American types with which the present form 



