EOCENE ECHINODERMATA. 113 



Class ECHINOLDEA. 



Subclass REGULARIA ENDOBRANCHIATA. 



Order CIDAROIDEA. 



Family CIDARID.E. 



Genus CIDARIS Leske. 



Cidaris mitchelli Enimons. 



Plate LV, figures la-c. 



Cidaris mitchelli Emmons, 1858, Agriculture Eastern Counties: Kept. North Carolina Geol. Survey, p. 305, fig. 237. 

 Cidaris mitchelli Conrad, 1866, Check list, Eocene and Oligocene, p. 3. 

 Cidaris mitchelli Heilprin, 1884, Contrib. Tertiary geology, p. 17. 

 Cidaris mitchelli Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 693. 



Determinative characters. — Test large, thick, and of moderate height. Ambulacra rather 

 broad, somewhat undulating with four to six rows of granules between the poriferous avenues. 

 Interambulacra wide with 9 to 10 plates in each row, each plate bearing a single large circular 

 tubercle the areola of which is surrounded by a row of small tubercles. Miliary space covered 

 with numerous thickly radiated granules. 



Dimensions. — Diameter 53 millimeters; height 32 rnillirneters. 



Description. — The species is represented by a single specimen, the type described by 

 Emmons, which in many particulars is in an excellent state of preservation. The test is large, 

 thick, and circular in outline. It is of medium height. 



The ambulacra are rather broad and somewhat undulating, with four rows of granules 

 between the poriferous avenues toward the apical system and peristome, but with six rows on the 

 ambitus. The pores are oral and connected by deep furrows. 



The interambulacra are wide and bear two rows of large circular tubercles, the areolas of 

 which closely approach each other and are covered by a row of small tubercles. The tubercles 

 are round, depressed, and have much elevated and deeply perforated mamelons. 



Belated forms. — The species is most closely related to C. carolinensis but is somewhat lower, 

 the granules on its miliary space are smaller and differently distributed and its tubercles approach 

 each other more closely. Its areolas have a surrounding row of small tubercles which are absent 

 in C. carolinensis. 



Locality. — Craven County (?), N. C. (Emmons). 



Geologic horizon. — Trent marl, middle Eocene. 



Collection. — Williams College. 



Cidaris carolinensis Emmons. 



Plate LV, figures 2a-c. 



Cidaris carolinensis Emmons, 1858, Agriculture Eastern Counties: North Carolina Geol. Survey Rept., pp. 305-306, 



fig. 238. 

 Cidaris carolinensis Conrad, 1866, Check list, Eocene and Oligocene, p. 31. 

 Cidaris carolinensis Heilprin, 1884, Contrib. Tertiary geology, p. 17. 

 Cidaris carolinensis Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 69S. 



Determinative characters. — Test large, thick, and rather tall. Ambulacra rather broad, 

 somewhat undulating, with four rows of granules between the poriferous avenues. Interambu- 

 lacra wide, each with two rows of large circular tubercles, 10 to 11 in each row. Miliary space 

 covered with numerous thickly set granules. 



Dimensions. — Diameter 60 millimeters ; height 35 millimeters. 



Description. — The type specimen of Emmons is the only representative of this species that 

 has been available for study. Although somewhat crushed the portions preserved are in an 

 excellent state of preservation. The test is of rather large size, thick, and somewhat taller than 

 in most species of Cidaris. 



