58 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



No figures are given and the incompleteness of the description leave some question as to- 

 whether the reference of this form to Hemipedina is correct. 



Dimensions. — Diameter 25 millimeters; height 11 millimeters; width of peristome 7 to 8 

 millimeters; width of periproct 3.5 millimeters. 



Locality. — About a mile east of Denison, Grayson County, Tex. 



Geologic horizon. — Main Street limestone member of the Denison formation of Washita 

 group, Comanche series, Cretaceous. 



Collection. — Baylor University. 



Family DIPLOPODIIDjE. 



Genus DIPLOPODIA McCoy. 



Diplopodia taffi Cragin. 



Plate XX, figures 2a-e. 



Diplopodia taffi Cragin, 1893, Geol. Survey Texas Fourth Ann. Jtept., pp. 148, 149, PL XLVI, fig. 3. 



Determinative characters. — Test large, subcircular, depressed; lower surface flattened; 

 ambulacra with two vertical rows of primary tubercles perforate and crenulate, slightly smaller 

 than the interambulacral tubercles, pairs of pores biserial above the ambitus toward the apical 

 system and at the peristome, iniserial below the ambitus ; interambulacral plate with eight rows 

 of primary tubercles at the ambitus ; peristome small with well-marked incisions. 



Dimensions. — Diameter 59 millimeters; height 26 millimeters. 



Description. — This very beautiful species is one of the largest in the Lower Cretaceous. It 

 is represented by a number of specimens although far less common than Cyphosoma texanum, with 

 which it is found associated. 



The test is depressed and slightly pentagonal in outline. The lower surface is flattened, 

 the sides somewhat inflated, and the upper surface slightly elevated. 



The ambulacra are of moderate width, with two vertical rows of perforate and crenulate 

 primary tubercles, which are slightly smaller than the interambulacral tubercles. The pore 

 pairs are biserial from the ambitus above toward the apical system and at the peristome, but 

 uniserial from the ambitus toward the peristome. 



The inter ambulacra are broad, with six rows of large and two of small primary tubercles at 

 the ambitus, the small tubercles, one row on each side outside the large tubercles, being confined 

 to that region. The outer rows of large tubercles likewise do not reach the peristome and apical 

 system. A broad and somewhat depressed area follows the median section of the ambulacra. 



The apical system is not large and its rays penetrate deeply the interambulacra. 



The peristome is small, with ten rather deep branchial incisions. 



Belated forms. — This species shows some similarity to D. streeruvifzi, but is not quite as 

 much elevated aborally. 



Localities. — North San Gabriel River, 3 miles above Georgetown (type), Benbrook, Tarrant 

 County, and Blum, Hill County, Tex. 



Geologic horizon. — Comanche Peak limestone of Fredericksburg group, Comanche series, 

 Cretaceous. 



. Collections. — Geological Survey of Texas; U. S. National Museum. 



Diplopodia streeruvitzi Cragin. 



Plate XX, figures 3a-c. 



Diplopodia streeruvitzi Cragin, 1893, Geol. Survey Texas Fourth Ann. Kept., pp. 147, 148, PL XXIV, fig. 11, PL XXV, 

 figs. 9-10. 



Determinative characters. — Test medium size, subcircular, depressed, upper and lower sur- 

 faces flattened; ambulacral plates with two vertical rows of primary tubercles, pairs of pores 

 simple except toward apical system and peristome where they are biserial; interambulacral plates 

 with six to eight vertical rows of primary tubercles at the ambitus ; peristome small. 



Dimensions. — Diameter 25 to 50 millimeters; height 12 to 18 millimeters. 



