MIOCENE ECHINODEKMATA. 181 



Ccelopletirtjs sloani Clark, n. sp. 

 Plate LXXXIV, figures 5a-b. 



Determinative characters. — Test moderate size, circular, elevated. Ambulacra narrow, 

 each with two rows of primary tubercles which rapidly diminish in size above the ambitus. 

 Interambulacra with median space on upper surface without tubercles. Apical system prom- 

 inent. Peristome small. Periproct large, subpentagonal. 



Dimensions. — Diameter 27 millimeters; height 15 millimeters. 



Description. — This species has a test of medium size, circular in ambital outline and much 

 elevated. The apex is high and the upper surface slopes regularly and rapidly from the ambitus 

 to it. The lower surface is concave. 



The ambulacra are narrow, the poriferous zones being nearly straight and flush. Each am- 

 bulacrum has two rows of primary tubercles imperforate and noncrenulate, which are very much 

 larger at the ambitus than above or below. These tubercles are veiy rapidly reduced in size 

 on the upper surface and entirely disappear or are replaced by small secondaries as the apical 

 system is approached. 



The interambulacra have similar tubercles to those of the ambidacra, the two outer rows 

 only on each area continuing to the apical system. 



The apical system is simple and distinct. The peristome is small and the periproct large 

 and of subpentagonal outline. 



Related forms. — C. sloani is quite distinct from 0. improcerus, the only other Miocene species 

 known at the present time. It is much higher and has a quite different distribution of the 

 primary tubercles. 



Locality. — Basticks Landing, Great Peedee River, S. C. 



Geologic horizon.— Miocene. 



Collection. — U. S. National Museum (166488). 



Suborder ECHININA. 

 Family TRIPLECHINID.E. 



Genus PSAMMECHINTTS Agassiz. 



PSAMMECHINUS PHTLANTHROPTTS (Conrad). 



Plate LXXXIV, figures 6a-c. 



Echinus philanthropus Conrad, 1S43, Acad. Nat. Sci. Philadelphia Proc, vol. 1, p. 310. 



Echinus ruffini Forbes, 1845, Geol. Soc. London Quart. Jour., vol. 1, p. 426, figs. a-d. 



Echinus ruffini Forbes, 1845, Geol. Soc. London Proc, vol. 4, p. 560, text figs. 



Echinus philanthropus Conrad, 1846, Am. Jour. Sci., 2d ser., vol. 1, No. 2, p. 220. 



Psammechinus ruffini Desor, 1858, Synopsis echinides fossiles, p. 121. 



Echinus ruffini Emnions, 1858, Agriculture eastern counties : North Carolina Geol. Survey, pp. 306, 307, figs. 239a-d. 



Psammechinus philanthropus Meek, 1864, Check list, Miocene, p. 2. 



Psammechinus ruffini Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 75. 



Determinative characters. — Test small, subhemispherical, tumid at the ambitus, somewhat 

 depressed above, nearly flat below. Ambulacra with two main rows of primary tubercles extend- 

 ing from peristome to apical system, with a thick median row a portion of distance, poriferous 

 zones narrow; pore pahs in triplets in oblique rows. Interambulacra with four regular and two 

 median somewhat irregular rows of subequal primary tubercles at ambitus, the latter reduced 

 toward peristome and apical system. Peristome rather wide, branchial incisions distinct. 



Description. — This species which was described by Conrad in 1843 from material secured 

 near Smithfield, Va. ? was described by Forbes two j r ears later as E. ruffini. The test is small 

 and subhemispherical, with a nearly circular ambital outline. It is tumid at the ambitus, some- 

 what depressed above and nearly flat below, with a slight depression near the peristomial margin. 



The ambulacra are rather narrow, the median portion of each area being covered with two 

 main rows of primary tubercles, imperforate and noncrenulate, which extend from the peristome 



