118 MESOZOIC AND CENOZOIC ECHINODEKMATA OF THE UNITED STATES. 



Suborder DIADEMINA. 

 Family CYPHOSOMATIDiE. 



Genus ORTHECHINUS Gauthier. 



Orthechinus pretiosus Clark, n. sp. 

 Plate LVI, figures 2 a-b. 



Determinative characters. — Test small, depressed, circular. Ambulacra wide, with two rows 

 of low primary tubercles, crenulate and imperforate; poriferous avenues straight, pore pairs 

 uniserial, with three pairs to each plate. Interambulacra with two rows of primary tubercles 

 similar to those of ambulacra and with additional smaller tubercles and granules. Apical 

 system large. Periproct large. 



Dimensions. — Diameter 20 millimeters; height 8 millimeters. 



Description. — A single crushed specimen of this species has been found. The test is small 

 depressed, and circular in ambit al outline. The ambulacra are wide with two rows of crenulate 

 and imperforate small primary tubercles, whicii are somewhat indistinct on account of their 

 relatively small, low mamelons and small areolas. Smaller tubercles and granules are also 

 found. The poriferous avenues are straight, the pore pairs uniserial with three pairs to each 

 compound plate. 



The interambulacra have two rows of primary tubercles similar to the ambulacra together 

 with smaller tubercles. The miliary space is covered with irregularly dispersed granules. 



The apical system is large, pentagonal in outline, and with large genital plates. The 

 periproct is large. 



Locality. — Dead Level, Choctaw County, Ala. 



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



Collection. — TJ. S. National Museum (146455). 



Suborder ECHININA. 

 Family TRIPLECHINIDjE. 



Genus ECHINUS Linne. 



Echinus exerceus De Gregorio. 



? Echinus sp. Aldrich, 1886, Alabama Geol. Survey Bull. 1, p. 49. 



Echinus exerceus De Gregorio, 1890, Alabama Mon. faune eocenique, p. 252, PI. XLIV, fig. 3. 



Echinus exerceus Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 697. 



Description. — No material representing this species was aA^ailable for study. De Gregorio 

 gives the following description: "Aculeus exilis, oblongus, sub lente minutissime eleganter 

 punctulatus reticulatusque, inferne ad basim turgidus." 



Locality. — Near Claiborne, Ala. (De Gregorio). 



Geologic horizon. — Claiborne group, middle Eocene. 



Collection. — De Gregorio. 



Echinus (?) sp. 



Plate LVI, figure 3. 

 Diadematoid spines, Clark and Martin, 1901, Maryland Geol. Survey, Eocene, p. 232, PI. LXI, fig. 2. 



Description. — Several small, thin echinoid spines, the generic relations of which can not be 

 with certainty determined, have been found in the Eocene deposits of Maryland and Virginia. 

 They are doubtfully referred to Echinus. 



Localities. — Near South River and Severn River, Md. ; Potomac Creek, Va. 



Geologic horizon. — Aquia formation, lower Eocene. 



Collection. — Johns Hopkins University (T 2000). 



