86 MESOZOIC ECHiNODERMATA OF THE UNITED STATES. [bull. 9?. 



inward between the anterior and posterior paired ambulacra. Apical 

 disk small, comi)act. Month opening transversely oval near anterior 

 margin. Anal opening oval, sujiramarginal. 



Dimensions. — Length, 1;^ inches; width, 1^ inches; height, |^ inch. 



Description. — This species has an oval, ci)rdate test, that is very much 

 elevated in tbe posterior portion. Anteriorlj'- the upper surface slopes 

 rapidly, so that the margin is much thinned down, losing the full round 

 aspect of the i)reviously described foims. The sharp ridge on the pos- 

 terior portion of tbe test is terminated by a nearly vertical truncation 

 of the posterior margin. The base is flat, save for the peristomial de- 

 pression. 



The ambulacral areas are narrow. The poriferous zones are petaloi- 

 dal, straight, and deeply depressed on the upper surface. The unpaired 

 ambulacrum is placed in the anterior sulcus and but slightly exceeds 

 the other areas in width. The petals of the autero-lateral pair are twice 

 the length of the postero lateral. The pores of the paired ambulacra 

 are elongated and separated (PI. xlvt. Fig. 2e), those of the single am- 

 bulacrum sunxll, oval, and approximated (PI. xlvi. Fig. 2/). 



The surface of the test is covered with sjuall tubercles, between 

 which are numerous minute granules. The i^eripetalous fasciole is dis- 

 tinct and bent outwards between the anterior and posterior paired 

 ambulacra. 



The ax)ical disk is small and situated posterior to the center of the 

 upper surface. The anterolateral genital plate is very large and widely 

 separates the posterior pair of oculars. The posterolateral genitals 

 have large perforations (PI. xlyi. Fig. 2(j). 



The mouth opening is tiansversely oval, bilabiate, with a prominentlj^ 

 projecting lower lip. The anal opening is large and situated at the 

 upper part of the truncated face of the posterior margin. 



Related forms. — It is separated from Hemiaster parastatus, with which 

 it is found, by the narrower anterior groove, more central apical disk, 

 less inflated sides, sharper posterior keel, and straight ambulacral 

 plates. 



Locality and geological horizon. — Hemiaster ungula is from the yellow 

 limestone of the middle marl bed (upper Cretaceous) of Timber creek, 

 New Jersey. 



Collections. — Philadelphia Academy of Natural Sciences; American 

 Museum of Natural History, New York. 



Hemiaster texanus Roemer. 



Plate XL VII, Figs la-i. 



Hemiaster texanus Roemer, 1849. Texas, etc., p. 393. 



Hemiaster texanus Roemer, 1852. Die Kreidebildungeu von Texas, p. 85. PI. 10, Fig. 4. 



Hemiaster americanus Giebel, 1853. Jaliresber. d. Naturw. Ver. in Halle, p. 372, 373. 



Hemiaster texanus Gabb, 1859. Cat. Invert. Fossils, Cretaceous, p. 19. 



Hemiaster texanus Meek, 1864. Smith. Misc. Coll., vol. 7 (177), p. 3. 



Hemiaster texanus Clark, 1891. Johns Hopkins Uuiversitj' Circulars, No. 87, p. 77. 



