CRETACEOUS ECHINODEKMATA. 95 



Determinative characters. — Test oval, cordate, declining anteriorly, elevated slightly posteri- 

 orly; anterior sulcus broad and deep, producing groove in margin. Ambulacra broadly de- 

 pressed on upper surface; antero-lateral pair bent backward in upper part; unpaired ambula- 

 crum very broad. Apical system compact, the four genitals distinctly perforated. Peristome 

 large, transversely oval, bilabiate. Periproct large, oval, at center of truncated surface of 

 posterior margin. 



Dimensions. — Length 22 to 38 millimeters; width 21 to 36 millimeters; height 15 to 20 

 millimeters. 



Description. — This important species is broadly cordate and slightly depressed on the upper 

 surface ; base flat. Posterior to the apex there is a sharp ridge that declines gradually toward the 

 obliquely truncated margin. Anteriorly the upper surface declines toward the anterior border. 



The ambulacra are broad, very unequal, and depressed in the petaloidal portions. The 

 poriferous zones are broad, the pores of the paired ambulacra elongated, those of the single ambu- 

 lacrum round and approximated. The petals of the anterolateral pair are bent backward in 

 their upper part and are nearly twice the width of the posterolateral pair. The single ambula- 

 crum is very broad, the poriferous zones widely separated. 



The surface of the test is covered with small tubercles that are perforated and for the most 

 part crenulated. A microscopic granulation fills the intertubercular space. 



The apical system is small and compact and situated near the center. The four genital 

 plates are distinctly perforated; the right anterolateral is larger than the others and serves as 

 the madreporite. The five oculars are wedged between the genitals and are deeply cut by the 

 upper portions of the ambulacra. 



The peristome is large, transversely oval, and bilabiate. The periproct is large, oval and 

 situated in the center of the truncated surface of the posterior margin. 



Related forms. — Under the name of Hemiaster americanus, Giebel published in 1853 the 

 description of a new species of Hemiaster which he states can be with difficulty distinguished 

 from H. texanus. It is considered identical in the present report since the differences seem 

 hardly to warrant the establishment of a new species. Periaster australis, described by Gabb 

 from Peru, as far as the figures and description show, must be a Hemiaster, and to all appear- 

 ances is closely allied if not identical with H. texanus. 



Localities. — At waterfall of Guadalupe below New Braunfels (type), Fairview (figured speci- 

 men), and Austin, Tex. 



Geologic horizon. — Austin chalk, Upper Cretaceous. 



Collections. — U. S. National Museum; Johns Hopkins University (T 3013). 



Hemiaster humphreysanus Meek and Hayden. 

 Plate XLIX, figures 2a-f. 



Hemiaster (?) humphreysanus Meek and Hayden, 1857, Acad. Nat. Sci. Philadelphia Proc., vol. 9, pp. 147, 148. 



Hemiaster (?) humphreysanus Gabb, 1859, Cat. Invert. Fossils Cretaceous, p. 19. 



Hemiaster (?) humphreysanus Meek, 1864, Smithsonian Misc. Coll., vol. 7 (177), p. 3. 



Hemiaster humphreysanus Meek, 1876, U. S. Geol. and Geog. Survey Terr. Final Rept., vol. 9, pp. 5, 6, PI. X, figs. la-g. 



Hemiaster humphreysanus Clark, 1891, Johns Hopkins Univ. Circ., vol. 10, No. 87, p. 77. 



Hemiaster humphreysanus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 



Hemiaster humphreysanus Clark, U. S. Geol. Survey Bull. 97, p. 88, PI. XLVIII, figs. la-f. 



Determinative characters. — Test oval, cordate; upper surface high, flat, with broad, vertical 

 truncation on posterior margin, and long anterior groove; base flat; sides rounded. Ambulacra 

 in deep furrows that reach to the edge of the elevated sides. Apical system large and compact, 

 posteriorly situated. Peristome small, transversely oval, and bilabiate. Periproct oval, situ- 

 ated high on posterior margin. 



Dimensions. — Length 32.5 millimeters; width 31.5 millimeters; height 20.5 millimeters. 



Description. — The absence of distinct fascioles on the type specimens of this species caused 

 Meek and Hayden to place it doubtfully in the genus Hemiaster, to which beyond doubt it belongs. 

 The test is full, the sides rounded, and the high upper surface distinctly flattened. The base is 



