114 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



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

 the poriferous avenues on the upper and lower surfaces, which become increased to six at the 

 ambitus. The pores are oval in shape. 



The interambulacra are wide, each with two rows of large circular tubercles that however 

 leave a wide miliary space on each plate that is thickly set with granules of very uniform size 

 throughout. The tubercles are round and deeply depressed. The boss is smooth and the mame- 

 lons deeply perforated. 



Related forms. — This species is closely related to C. mitcheUi but is evidently taller and has 

 larger granules somewhat differently dispersed. Its tubercles are more widely separated than 

 those of C. mitcheJli, and its areolas lack the surrounding row of small tubercles. 



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



Geologic horizon. — Trent marl, middle Eocene. 



Collection. — Williams College. 



Cidaeis pratti Clark, n. sp. 

 Plate IV, figure 3. 



Determinative characters. — Test small, thin, rather high, circular. Ambulacra narrow 

 undulating, two rows of granules between the poriferous avenues; pores nearly round. Inter- 

 ambulacra wide, each with two rows of tubei - cles; each tubercle round, depressed, with crenu- 

 lated boss and perforated mamelon and with areolas surrounded by row of small tubercles. 



Dimensions. — Diameter 18 (?) millimeters; height 15 (?) millimeters. 



Description. — The only specimens available for study consist of fragments of tests, chiefly 

 of detached plates. The test is small and thin, rather high, and apparently circular in outline. 



The ambulacra are narrow and undulating. The pores are nearly round. Two rows of 

 small granules occur between the poriferous avenues. 



The interambulacra are wide, each with two rows of tubercles which largely occupy the area 

 of the plates. The miliary space is very small and covered with granules. Each tubercle has a 

 depressed areola surrounded by a row of small tubercles. The boss is crenulated and the mame- 

 lon perforated. 



Related forms. — The species is unique and differs widely from the other Tertiary species. 

 It is more closely related to C. mitchelli than to C. carolinensis. 



Locality. — Wilmington, N. C. 



Geologic horizon. — Castle Hayne limestone, upper Eocene or Oligocene. 



Collection.— U. S. National Museum (164663). 



Cidaeis mereiami Arnold. 

 Plate LV, figure 4. 



Cidaris rnerriami Arnold, 1908, U. S. Nat. Mus. Proc, vol. 34, p. 359, PI. XXXII, fig. 8. 

 Cidaris rnerriami Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 696. 



Determinative characters. — Test wanting. Spine subcircular in cross section, tapering slightly ; 

 surface with 13 or 14 prominent ribs separated by narrow grooves; nodes well defined. 



Dimensions. — Longest fragment; length 20 millimeters; maximum diameter "4.5 milli- 

 meters. 



Description. — Arnold, in his description of this species, says: 



The test of this species is unknown, but the abundance and well marked characteristics of the fragments of the 

 Bpines has been deemed of enough importance to justify a specific name. Seven specimens have been obtained at the 

 type locality, each showing the characters described above. 



Spines subcircular in cross section, as much as 4 millimeters in diameter and probably over 40 millimeters in 

 length, tapering very slightly; surface sculptured by 13 or 14 prominent, narrow, nodose, ridgelike, longitudinal ribs 

 separated by narrow, deeply incised grooves; the nodes are well defined, especially in the younger stages of growth, and 

 are subelliptical in cross section, their longer axis being parallel with the axis of the spine. 



