CRETACEOUS ECHINODEEMATA. 59 



Description. — This species is not numerous, and the known forms are confined to El Paso 

 County, Tex. The test is very nearly circular in ambital outline, is depressed, and is distinctly 

 flattened both adorally and aborally. 



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

 primary tubercles of about the same size as the interambulacral tubercles. The poriferous zones 

 are wide above the ambitus but narrow at the ambitus and below until near the peristome. The 

 pore pahs are biserial aborally. There is much crowding of the pore pahs at the peristome. 



The interambulacra are wide with six or eight rows of primary tubercles sinnlar to those of 

 the ambulacra. The outer rows are somewhat irregular in distribution and gradually disappear 

 aborally. 



The apical system is of medium size. The peristome is small. 



Localities. — Sierra Blanca peaks (type) and near Kent, El Paso County, Tex. 



Geologic horizon. — Washita group of the Comanche series, Cretaceous. 



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



Family CYPHOSOMATID,E. 



Genus CYPHOSOMA Agassiz. 



Ctphosoma hilli Clark. 



Plate XIX, figures 2a-g. 



Pseudodiadt ma hilli Clark, 1S91, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 76. 

 Diplopodia hilli Clark, 1S93, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Diplopodia hilli Clark, 1S93, U. S. Geol. Survey Bull. 97, pp. 50, 51, PI. XVI, figs. 2a~g. 

 Diplopodia hilli Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 147. 



Determinative characters. — Test subpentagonal, depressed; sides inflated; upper and lower 

 surfaces flattened. Ambulacra prominent, straight, with two rows of primary tubercles, twelve 

 or thirteen in each row; poriferous zones narrow, with slight increase in width toward the apical 

 system; pores in single pairs below but biserial on the upper surface. Interambulacra with two 

 rows of primary tubercles of equal size with those of the ambulacra. Peristome narrow, circidar. 

 Discal opening broad, pentagonal. 



Dimensions. — Diameter 20 millimeters; height 8 millimeters. 



Description. — The test has a subpentagonal outline, the projecting ambulacra occupying the 

 angles. It is depressed on both the upper and lower surfaces, the latter becoming somewhat 

 concave toward the peristome. The sides are moderately inflated. 



The ambulacra are broad, very prominent, and furnished with two rows of large tubercles, 

 twelve or thirteen in each row, that decrease rapidly from the ambitus toward the apical system 

 and peristome. The poriferous zones are narrow and lanceolate. The pores are arranged in 

 single pahs on the lower surface, but from the ambitus to the apical system are increased slightly 

 in number, and near the apical system become biserial. The interambulacra are narrow and 

 appear flattened as compared with the slightly projecting ambulacra. They are provided with 

 two rows of primary tubercles of equal size with those of the ambulacra. There are ten or eleven 

 in each row. The areolas are narrow, circular, and elevated, the bosses prominent and distinctly 

 crenulated, and the mamelons deeply perforated. The tubercles are somewhat widely separated 

 and the intervening space is covered with small secondary tubercles and sparsely scattered 

 granules. 



The peristome is broad, depressed, and circular. It is divided by ten incisions into well- 

 defined lobes, those of the ambulacra broader and extending farther into the opening than the 

 others. 



The chscal opening is pentagonal, the angles occurring at the point of the medial suture of 

 the interambulacra. 



This species which was earlier referred to Diplopodia has been shown to belong to the genus 

 Cyphosoma. Better material has furnished specimens in which the morphology of the ambulacra 

 demiplates can be clearly seen. 



