158 MESOZOIC AND CENOZOIC ECHINODERMATA OP THE UNITED STATES. 



ClDARIS GEORGIANA Clark, 11. Sp. 

 Plate LXXIII, figure 4. 



Determinative characters. — Test moderately high, subcircular, medium size. Ambulacra 

 wide, with large primary tubercle on each plate, the tubercles on contiguous plates closely 

 approximate, wide miliary space between the rows of tubercles. 



Dimensions. — Diameter 3S (?) millimeters; height 25 (?) millimeters. 



Description. — The test of this species is only partly preserved. It shows, however, the 

 chief determinative characters. It is evidently unlike any other form hitherto described. 

 The test is of medium size, moderately high, and subcircular in ambital outline. The full 

 height and diameter can not be with certainty determined. The ambulacra are rather broad 

 and straight, with four rows of granules between the poriferous zones. 



Locality. — Muckafoonee Creek, Ga. 



Geologic horizon. — Vicksburg formation, lower Oligocene. 



Collection. — U. S. National Museum (166485). 



Cidaris branneei Arnold. 

 Plate LXXIII, figure 5. 



Cidaris branneri, Arnold, 1903, U. S. Nat. Mus. Proc, vol. 29, pp. 363, 364, PI. XXXIII, fig. 5. 

 Cidaris branneri Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 698. 



Description. — Arnold says : 



Test unknown. Spines, long, slender, circular in cross section, attaining a length of at least 25 millimeters and a 

 diameter of over 2 millimeters. Surface of spine smooth for about one-fifth its length from the base; above this it is 

 ornamented by ten longitudinal rows of elongated nodes or granules which are barely connected near the smooth 

 portion, but which partake more and more of the character of nodose ribs toward the distal end; the last one-fifth of the 

 spine is ornamented by five prominent, slightly nodose ribs; the extreme end is blunt and rounded; collar at base only 

 faintly developed. 



The spines of this species are easily distinguishable from those of C. merriami, new species, from the Eocene, by 

 their smaller size, fewer but much more prominently nodose longitudinal ribs, and smooth basal portion. No complete 

 spine of C. merriami was obtained, so that the smooth basal section may possibly be a characteristic of this latter species 

 as well as of C. branneri. 



Dimensions. — Length 20 millimeters; diameter, basal end 2.2 millimeters, distal end 1.1 

 millimeters. 



Localities. — Santa Cruz quadrangle, Santa Cruz Countj^, locality No. 109 on Bear Creek, 4 

 miles above its confluence with the San Lorenzo River, Cal. 



Geohgic horizon. — San Lorenzo formation, upper Oligocene. 



Collection. — U. S. National Museum (1056). - 



Subclass REGULAEIA ECTOBRANCHIATA. 



Order DUDEMOIDEA. 



Suborder ARBACINA. 



Family ARBACIIDvE. 



Genus CCELOPLETTRU S Agassiz. 



CCELOPLEURUS ALDRICHI Clark, 11. Sp. 



Plate LXXIII, figures 6a-b, 7a-c. 



Determinative characters. — Test large, subpentagonal, tumid at ambitus, depressed above, 

 nearly flat below. Ambulacra narrow, the two rows of primary tubercles becoming very small 

 toward the apex; poriferous zones narrow and straight, the pore pairs uniserial. Interam- 

 bulacra wide, each with several rows of large primary tubercles at ambitus reduced to two 

 around peristome and on upper surface, leaving wide median area above. Tubercles with flat 

 areolas and large imperforate mamelons. Peristome with very slight branchial incisions. 



