88 MESOZOIC AND CENOZOIC ECHIXODEKMATA OP THE UNITED STATES. 



found, and it may perhaps be wiser to regard the difference as varietal rather than specific. This 

 species is related to E. mexicanus, described by Cotteau in 1890, from material obtained from 

 Mexico. 



Localities. — Near Austin (type) and Glen Rose and other localities in Texas. 



Geologic horizon. — Glen Eose limestone of the Trinity group, Comanche series, Cretaceous. 



Collections. — TJ. S. National Museum (12237); Geological Survey of Texas. 



Genus HEMIASTER. Desor. 



Hemiaster elegans Shumard. 



Plate XLI, figures la-c; Plate XLII, figures la-h; Plate XLIII, figures la-f. 



Hemiaster elegans Shumard, 1853, Pal. Expl. Red River of Louisiana in 1852, p. 210, PI. II, figs. 4a-c. 



Toxaster elegans Gabb, 1859, Cat. Invert. Fossils Cretaceous, p. 19. 



Toxaster elegans Meek, 1864, Smithsonian Misc. Coll., vol. 7 (177) p. 3. 



Macraster texanus Roemer, 1888, Neues Jahrb., vol. 1, pp. 191-195, PI. VI, figs. 1-4. 



Epiaster elegans Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 77. 



Epiaster elegans Clark, 1893, Johns Hopkins Univ. Circ. , vol. 12, No. 103, p. 52. 



Epiaster elegans Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 80-82, PI. XLI, figs, la-b; PI. XLII, figs, la-b; PI. XLIII, 



figs. la-e. 

 Epiaster electus Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 152. 

 Epiaster elegans Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 152. 



Epiaster elegans var. nov. prxnumtius Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 152. 

 Epiaster elegans, Hill and Vaughan, 1898, U. S.. Geol. Survey Eighteenth Ann. Rept., pt. 2, PI. LVI, fig. 3. 

 Epiaster elegans Hill, 1901, U. S. Geol. Survey Twenty-first Ann. Rept., pt. 7, pp. 226, 251, 260, PI. XXXVI, fig. 4. 



Determinative characters. — Test large, oblong, cordiform, flattened both above and below; 

 sides rounded, with a shallow anterior groove and truncated posterior margin. Ambulacra 

 subpetaloidal, depressed; poriferous zones straight, pores with elongated, slitlike openings. 

 Apical system small. Peristome transversely oval, situated near the anterior margin. Peri- 

 proct oval, situated on the truncated posterior margin. 



Dimensions. — Length 30 to 110 millimeters; width 25 to 100 millimeters; height 15 to 55 

 millimeters. 



Description. — Roemer in 1888 established a new genus and species, Macraster texanus, for a 

 form that is identical with Hemiaster elegans described by Shumard in 1853. There does not 

 seem to be a sufficiently wide difference between the characters assigned to Macraster and those- 

 properly belonging to Hemiaster to warrant the acceptance of the former genus for the present 

 species. 



The test is very large and flattened on both the upper and lower surfaces. The sides are 

 round. The groove on the anterior face is shallow and cuts the margin lightly. The posterior 

 face is obliquely but not broadly truncated. 



The ambulacral areas are nearly equal, depressed, with a distinct furrow on the upper sur- 

 face. The poriferous zones are long, wide, and straight, and the pores consist of slitlike openings. 

 The zones are subpetaloidal on the upper surface, reaching quite to the upper margin of the 

 rounded sides. The unpaired ambulacrum is narrower than the others; the pores are smaller 

 and more closely approximated. 



The surface of both areas is covered with minute tubercles, between which are microscopic 

 granules. 



The apical system is small, compact, and consists of four large perforated genital plates and 

 five small oculars. 



The peristome is transversely oval and situated near the anterior margin. 



The periproct is large, oval, and situated on the truncated face of the posterior margin. 



This and the succeeding species are now referred to the genus Hemiaster, as better material 

 has shown that peripetalous fascioles are present although poorly developed and commonly 

 destroyed on most specimens. 



Related forms— H. elegans is most nearly related to H. whitei, but is separated from it by its 

 great size, its excessively long subpetaloidal areas, and the position of its periproct, which is on 



