OLIGOCENE ECHINODERMATA. 159 



Dimensions. — Specimen A: Diameter 38 millimeters; height 20 millimeters. Specimen B: 

 Diameter 28 millimeters; height 12 millimeters. 



Description. — The species is characterized by a rather large test, with subpentagonal out- 

 line. It is tumid at the ambitus and depressed on the upper surface. It is nearly flat below. 

 The ambulacra are narrow, each bearing two rows of primary tubercles that diminish rapidly 

 in size from the ambitus toward the apex. The poriferous zones are narrow, the pore pairs 

 being uniserial and somewhat crowded toward the apex. The interambulacra are wide with 

 several rows of primary tubercles at the ambitus which become reduced to twojoward the peri- 

 stome and above the ambitus, where a broad median area devoid of tubercles occurs. The 

 peristome is small with slight branchial incisions. 



The several specimens examined are much broken and the surfaces much worn. 



Locality. — Perdue Hill, Ala. 



Geologic horizon. — St. Stephens limestone (upper portion), lower Oligocene. 



Collection. — U. S. National Museum (T. H. Aldrich). 



Suborder DIADEMINA. 

 Family CYPHOSOMATIDiE. 



Genus GAGARIA Duncan. 



Gag aria Americana Clark, n. sp. 



Plate LXXIII, figures 8a-b. 



Determinative characters. — Test small, circular, tumid, subhemispherical, concave below. 

 Ambulacra narrow, each with two rows of small primary tubercles, perforate and crenulate; 

 each compound plate with three pairs of pores. Interambulacra wide, each with two rows of 

 primary tubercles. Apical system large, flush. 



Dimensions.— Diameter 14 millimeters ; height 8 millimeters. 



Description. — This beautiful form has a very small test, with a circular ambital outline. 

 It is tumid, subhemispherical, rather depressed above, concave below. The ambulacra are 

 narrow, each area provided with two rows of perforate and crenulate primary tubercles which 

 are longest at the ambitus and reach to the apical system, gradually diminishing in size. The 

 poriferous zones are narrow, the pore pairs being three in number on each compound plate. 

 The interambulacra are broad, each carrying two rows of primary tubercles similar to the ambu- 

 lacra between which are many small secondaries and granules. The apical system is large and 

 flush. 



This species is based on a single specimen, the peristomial region of which is much damaged. 



Locality. — The Rocks, Clarke County, Ala. 



Geologic horizon. — St. Stephens limestone (upper portion), lower Oligocene. 



Collection. — U. S. National Museum (T. H. Aldrich). 



Suborder ECHININA. 

 Family TRIPLECHINIDiE. 



Genus ECHINUS Linne. 



Echinus ? sp. 

 Echinus sp. Cunningham, 1895, Am. Micr. Jour., vol. 16, pp. 193-196, figs. 



Description. — Small spines and fragments of plates are figured by Cunningham from "cal- 

 careous marl" in Clarke County, Miss., and referred to the genus Echinus. It is quite impossible 

 to determine definitely the generic relations of these forms. 



Locality. — Red Bluff station, Chickasawhay River, Clarke County, Miss. 



Geologic horizon. — Vicksburg limestone, lower Oligocene 



Collection. — K. M. Cunningham, Mobile, Ala. 



