82 MESOZOIC ECHINODERMATA OF THE UNITED STATES. [bull. 97. 



characteristic of the Fort Worth limestone, and is found at numerous 

 localities between Denison and El Paso. 



Collections. — U. S. National Museum; Johns Hopkins University; 

 Boston Society of Natural History; Texas Geological Survey; Prof. 

 Eobt. T. Hill. 



Epiaster Whitei Clark. 



Plate XLiii, Figs. 2a-d; Plate xliv, Figs. la-g. 



Toxa/ifer eJegans Gonrsid, 1857. U. S. and Mex. Bound. Surv. Kept., vol. 1, pt. 2, p. 146, 



PI. 21, Fig. la-e.i 

 Epiaster Whitei Clark, 1891. Johns Hopkins University Circulars, No. 87, p. 77. 



Determinative characters. — Test small, cordiform; upper surface con- 

 vex, elevated ; lower surface flat; sides inflated; apex forward of the 

 center. Ambulacra moderately broad; poriferous zones petaloidal, 

 pores with elongated openings; an tero- lateral i:)air bent slightly back- 

 ward in upper part. Apical disk oval. Mouth opening transversely 

 oval. Anal opening small, oval, situated high on posterior border. 



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



Description. — This species has been frequently confounded with 

 Unallaster texanus and Epiaster elegans. With the former it has little 

 in common beyond a certain similarity in outward form, while the points 

 of difference from the latter are less striking and will be shortly stated. 



The test is small and cordiform. The upjier 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 groovy at the center of the an- 

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



The ambulacral areas are moderately broad. The poriferous zones 

 are subi^etaloidal in their upper part, but this feature does'not continue 

 to the margin (PI. xlhi. Fig. 2(?). The pores in the paired ambulacra 

 are all of about equal size and equally spaced. In the unpaired ambu- 

 lacrum they are smaller and nearer together. The anterolateral pair 

 are bent slightly backward in their upi)er i3art. They are distinctly 

 larger than the j)ostero-laterals. 



The interambulacral areas are prominent and the surface of the plates 

 covered with minute tubercles and microscopic granules (PI. xliv, 

 Fig. Ic). 



The apical disk is small, com])act, and consists of four large iierforated 

 genital j)lates and five oculars. 



The mouth opening is transversely subpentagonal and situated near 

 the anterior margin (PI. xliv. Figs. Ift, 1/). 



The anal opening is small, oval, and situated high on the truncated 

 posterior margin (PI. xliii. Fig. 2h). 



Related forms. — In many particulars Epiaster Whitei is to be closely 

 associated with E. elegans. It is, however, more elevated, the ambu- 



* Figmed under the name i>t' Tlolaster elegant. 



