CRETACEOUS ECHINODEEMATA. 57 



perforated and crenulated tubercles, pore pairs in simple series doubling toward the peristome; 

 interambulacral plates with two rows of primary tubercles but slightly larger than the ambu- 

 lacral. Peristome small. 



Dimensions. — Diameter 23 millimeters; height 11.5 millimeters. 



Description. — The single specimen representing this species is small, subcorneal, depressed 

 on the aboral surface but tumid at the ambitus. It is apparently distinctly convex on the 

 adoral surface. 



The ambulacra are moderately narrow, with two rows of small, primary, perforate, and 

 crenulate tubercles. The pore pairs when seen are simple. The plates are compound, the 

 sutures being very indistinct. 



The interambulacra are much wider than the ambulacra and bear two rows of primary 

 tubercles which are similar to the ambulacral. The posterior interambulacrum is deeply incised 

 and depressed near the apical system which intrudes far into it. 



The large aboral scar indicates an apical system of considerable size. 



Locality.— Fort Worth, Tex. 



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



Collection. — Johns Hopkins University (T 3006). 



Genus COTTALDIA Desor. 



Cottaldia ROTULA Clark, n. sp. 

 Plate XX, figures la-d. 



Determinative characters. — Test small, tumid, subhemispherical, aboral and adoral surfaces 

 somewhat depressed; apical system small; ambulacral plates crowded with irregular rows of 

 small primary tubercles, perforate and noncrenulate, pore pairs in simple series. Interambula- 

 cral plates with numerous small irregularly disposed tubercles ; peristome small. 



Dimensions. — Diameter 15 millimeters; height 12.5 millimeters. 



Description. — The test is small, much inflated at the ambitus, subhemispherical. The 

 aboral surface is slightly depressed and the adoral surface more so. 



The ambulacra are narrow, with four rows of very small, perforate, and uncrenulate tuber- 

 cles at the ambitus. The narrow poriferous zones are uniserial. The compound plates are 

 composed of three primary plates with very indistinct sutures. 



The interambulacra are wide, the plates being low and slightly bent. A row of seven small 

 tubercles crosses each plate nearly horizontally at the ambitus but becomes reduced in number 

 toward the poles. These tubercles are similar in character to those on the ambulacra. 



The apical system and peristome are not preserved on the specimens examined. 



Locality. — Shoal Creek, Travis County, Tex. 



Geologic horizon. — Buda (Shoal Creek) limestone of the Washita group, Comanche series, 

 Cretaceous. 



Collection. — Johns Hopkins University (T 3007) ; U. S. National Museum. 



Genus HEMIPEDINA Wright. 



Hemipedina charltoni Cragin. 



Hemipedirta charltoni Cragin, 1894, Colorado Coll. Studies, vol. 6, pp. 41, 47, 50, 51. 

 Description. — Cragin describes this species as follows: 



Test small, round-pentagonal, arched above, concave below; apical disk and periproct moderately broad; peris- 

 tome considerably smaller in proportion to the test than in Pseudodiadema texanum Koemer; pore-belts straight, the pores 

 somewhat elongated in the direction of the belt, the pore pairs simple throughout and somewhat oblique; ambulacral 

 arese half as broad as the interambulacral, each ornamented with two rows of primary tubercles that are somewhat 

 smaller thau those of the row of largest tubercles on the interambulacral arese, each primary tubercle being subtended 

 by an irregularly polygonal string of smaller (secondary) ones; interambulacral arese with six rows of primary tubercles, 

 these being much larger in the middle row of each semiambulacrum than in the others, the primaries subtended by 

 secondaries for the most part in polygonal strings; surface of test closely granulated in (lie intervals between tubercles 

 oa both ambulacral and interambulacral area?. 



