JURASSIC ECHINODERMATA. 31 



may bo compared. C. californicus is not known by its test and comparisons are limited to the 

 spines. In 0. taylorensis the spines are long and cylindrical, while in C. californicus they are 

 short and thick set, and have a totally different surface decoration. 0. taylorensis differs from 

 C. plumasensis in its smaller miliary space and circular areolas. 



Locality. — Taylorsville, Plumas County, Cal. 



Geologic horizon. — Hardgrave sandstone, Lower Jurassic. 



Collection.— V. S. National Museum (30183). 



Cidaeis plumasensis Clark, n. sp. 

 Plate IV, figure 3. 



Determinative characters. — Test medium size. Ambulacra narrow. Interambulacra wide. 

 Tubercles large with oval depressed areolas, crenulated boss, and perforated mamelon. Miliary 

 space covered with coarse granules. 



Dimensions. — Height of largest ambulacral plate 10 millimeters; width 14 millimeters. 



Description. — Fragments of casts of the test of this species are found on a single slab of 

 sandstone. The most perfect impression is of three interambulacral plates with adjacent ambu- 

 lacral plates. It is evidently part of the test of a form of medium size. The ambulacra are 

 narrow but the impression of the plates is obscure. The interambulacral plates are much better 

 preserved and show large tubercles with oval areolas, somewhat depressed. The boss is crenu- 

 lated and the mamelon perforated. The miliary space is rather wide and is covered with coarse 

 granules. 



Locality. — Taylorsville, Plumas County, Cal. 



Geologic horizon. — Hardgrave sandstone, Lower Jurassic. 



Collection.— U. S. National Museum (31191). 



Subclass REGULARIA ECTOBRANCHIATA. 



Order DIADEMOIDEA. 



Suborder ARBACINA. 



Family HEMICIDARIDjE. 



Genus HEMICIDARIS Agassiz. 

 Hemicidaris intumescens Clark. 

 Plate IV, figures 4a-i. 



Hemicidaris intumescens Clark, 1893, Johns Hopkins Univ. Girc, vol. 12, No. 103, p. 51. 

 Hemicidaris intumescens Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 44, 45, PI. XII, figs. la-i. 



Determinative characters. — Test spheroidal, upper surface inflated, lower surface flat. Am- 

 bulacra moderately broad, increasing in width from the apical system to the peristome. The 

 tubercles at the peristome are nearly equal in size to those of the interambulacral areas, but 

 become greatly reduced in passing from the ambitus to the apical system. Interambulacra 

 rather wide, with two rows of large tubercles. Miliary space wide, covered with numerous 

 granules. Peristome moderately wide, with deep incisions. 



Dimensions. — Diameter 18 millimeters; height 12 millimeters. 



Description. — The very perfectly preserved molds of the species permit the taking hi gutta- 

 percha of all the details of form and structure. As the only representative of the genus in 

 American deposits it possesses considerable interest. The test is of moderate size, with a con- 

 vex and slightly inflated upper surface and nearly flat lower surface. The slightly flexuous 

 ambulacra broaden from the region of the apical disk toward the ambitus and slightly contract 

 again before the peristome is reached. The tubercles are prominent in the lower part of the 

 column, where several pairs attain a size nearly equal to those of the interambulacra. Minute 

 perforated granules succeed them above and continue as a double row to the apical system. The 



