CKETACEOUS ECHINODEKMATA. 89 



an obliquely truncated surface that opens downward instead of being, as in E. whitei, on a verti- 

 cal face that opens upward. 



Localities. — Fort Washita (type), Fort Worth (figured specimen), and numerous other locali- 

 ties in Texas. 



.Geologic horizon. — Fort Worth lhnestone of Washita group, Comanche series, Cretaceous. 



Collections. — U. S. National Museum (21S87); Johns Hopkins University; Boston Society 

 of Natural History; Geological Survey of Texas. 



Hemiaster whitei Clark. 



Plate XLIII, figures 2a-c; Plate XLIV, figures la-h; Plate XLV, figures la-d, 2a-f. 



Toxaster elegans Conrad, 1857, TJ. S. and Mex. Boundary Survey Rept., vol. 1, pt. 2, p. 146, PL XXI, figs, la-e. 1 



Epiaster whitei Clark, 1S91, Johns Hopkins Univ. Circ., vol. 10, No. 87, p. 77. 



E piaster whitei Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 



Epiaster whitei Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 82, 83, PL XLIII, figs. 2a-d; PL XLIV, figs. la-g. 



Epiaster hemiasterinus Cragin, 1S93, Geol. Survey Texas Fourth Ann. Rept., p. 153. 



Epiaster whitei Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 154. 



Epiaster hemiasterinus Cragin, 1894, Colorado Coll. Studies, vol. 5, pp. 45, 47. 



Epiaster whitei Hill, 1901, U. S. Geol. Survey Twenty-first Ann. Rept., pt. 7, p. 226. 



Determinative characters. — Test small, cordiform; upper surface convex, elevated; lower 

 surface flat; sides inflated; apex forward of the center. Ambulacra moderately broad, petaloi- 

 dal, pores with elongated openings; anterolateral pair bent slightly backward in upper part. 

 Apical system subcentral. Peristome transversely oval. Periproct small, oval, situated high 

 on posterior border. 



Dimensions. — Length 10 to 50 millimeters; width 8 to 45 millimeters; height 16 to 30 

 millimeters. 



Description. — The test is small and cordiform. The upper surface is distinctly elevated, the 

 apex occupying a point anterior to the center. The lower surface is flat with the exception of the 

 peristomial depression. The sides are inflated with a well-marked groove at the center of the 

 anterior face and a prominent truncated surface on the posterior margin. 



The ambulacra are moderately broad. The poriferous zones are subpetaloidal in their 

 upper part, but this feature does not continue to the margin. The pores in the paired ambulacra 

 are all of about equal size and equally spaced. In the unpaired ambulacrum they are smaller 

 and nearer together. The anterolateral pah' are bent slightly backward in then - upper part. 

 They are distinctly larger than the posterolaterals. The inter ambulacra are prominent and the 

 surface of the plates covered with minute tubercles and microscopic granules. The apical system 

 is small, compact, and consists of four large perforated genital plates and five oculars. The 

 peristome is transversely subpentagonal and situated near the anterior margin. The periproct 

 is small, oval, and situated high on the truncated posterior margin. 



Related forms. — In many particulars Hemiaster whitei is to be closely associated with H. 

 elegans. It is, however, more elevated, its ambulacral furrows are shorter, and its periproct is 

 differently situated. (See p. 88.) 



Localities.— Duck Creek, near Denison (type), and numerous other localities in Texas. 



Geologic horizon. — Fredericksburg group and lower part of Washita group, Comanche series, 

 Cretaceous. 



Collections. — U. S. National Museum (4544, 9732, 31202); Johns Hopkins University. 



Hemiaster bex4.ri Clark, n. sp. 

 Plate XLVI, figures la-e. 



Determinative characters. — Test small, upper surface nearly flat, elevated, lower surface 

 rounded; sides inflated; apex nearly central, posterolateral ambulacra very short, interam- 

 bulacra prominent. Peristome small, only slightly depressed, near anterior margin. Periproct 

 small, situated high on truncated surface of posterior margin. 



1 Figured under the name Holasler elegans. 



