176 MESOZOIO AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Schizaster Americana Clark, n. sp. 

 Plate LXXXII, figures/a-d. 



Determinative characters. — Test medium size, subpentagonal, as wide as long, upper surface 

 elevated posteriorly. Ambulacra narrow, the anterior deeply sunken in deep groove; tbe paired 

 ambulacra with short petals, the posterior about one-half the length of the anterior. Interam- 

 bulacra broad, prominent. Peristome near anterior margin, in well-marked depression. Peri- 

 proct high on truncated posterior margin, peripetalous and lateral fascioles clearly marked. 



Dimensions. — Length 39 millimeters; width 39 millimeters; height 25 millimeters. 



Description. — The species has a test of medium size, rather tall, subpentagonal, as wide as 

 long, sloping up from the anterior margin to the nearly central apical system, beyond which a 

 sharp rise continues toward the posterior margin, its highest point being about midway. 



The ambulacra are narrow, the anterior one situated in a deep, moderately wide groove that 

 indents the anterior margin. The paired ambulacra have deep short petals, the anterolateral 

 being about twice as long as the posterolateral. 



The interambulacra are broad and somewhat gibbous on the sides. The posterior inter- 

 ambulacrum is much elevated and rather narrow. The surface is covered with numerous small 

 but clearly distinct tubercles with small granules between them. The peripetalous and lateral 

 fasciole can be readily traced. 



The apical system is small and nearly central in position. The peristome is near the anterior 

 margin in a well-marked depression. The periproct is high on the truncated posterior margin. 



Localities. — Yost limekiln near Brandon station, Rankin County (type), and Clarke County, 

 Miss. ; 5 miles south of Ellaville, on EllaviUe-Americus public road, Georgia. 



Geologic horizon. — Vicksburg formation, lower Oligocene. 



Collection. — U. S. National Museum (165695) ; Geological Survey of Georgia. 



EitpatacxTJs floridanus Clark, n. sp. 

 Plate LXXXII, figures ^a-d; Plate LXXXIII, figures la-c, 2a-d. 



Determinative characters. — Testlarge, elongate, subcordiform, depressed, sloping from anterior 

 margin to point half way from apical system to posterior truncation. Ambulacra nearly flush, 

 poriferous zones somewhat sunken, paired ambulacra with long petals. Interambulacra with 

 large perforate and crenulate tubercles irregularly scattered over surface. Fascioles distinct. 

 Peristome small. Periproct large. 



Dimensions. — Specimen A: Length 65 millimeters; width 56.5 millimeters; height 31.5 

 millimeters. Specimen B: Length 67 millimeters; width 56 millimeters; height 30 millimeters. 

 Specimen C: Length 49 millimeters; width 39.5 millimeters; height 23 millimeters. 



Description. — A number of specimens of this striking form have been found in the Oligocene 

 of Florida. The test is large, elongate, subcordiform, and depressed. The upper surface slopes 

 from the low anterior margin gradually to the high posterior apex which is situated about half- 

 way from the apical system to the beginning of the posterior truncation. The lower surface is 

 nearly flat. 



The ambulacra are wide nearly flush and the poriferous zones somewhat sunken. The paired 

 ambulacra have long, closed_petals the posterolateral longer than the anterolateral. The pore 

 openings of the petaloidal portions are small and round, the pore pairs connected by deep furrows. 



The interambulacra consist of large plates covered somewhat irregularly with large per- 

 forate and crenulate tubercles, the greater number occurring in more or less horizontal rows along 

 the upper part of the plates above the ambitus. 



The apical system is anterior to the center of the upper surface, is small and nearly flush. 



The fascioles are distinct here and there. The peristome is small and semicircular. The 

 periproct is large, occupying much of the truncated surface. 



Related forms. — This species has many points of similarity to E. clevei Cotteau of St. Bar- 

 thelemy Island, although it differs in some minor particulars. It may prove to be the same 

 species. 



