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



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



DcHcription. — This typical EchinobrissiTs is of moderate size, some- 

 what depressed above, and subquadrate in marginal outline. The pos- 

 terior portion is broader than the anterior and distinctly lobed. The 

 base is concave. 



The ambulacral areas are narrowly lanceolate, and on the upper sur- : 

 face the poriferous zones are subpetaloidal (PI. xxvi, Fig. la). The 

 inner rows of pores are round, the outer oval, with acuminated inner 

 margins and obliquely idaced (PI. xxvi, Fig. 1/). The interambulacral 

 areas are formed of broad plates that bear numerous small perforated 

 and mammillated tubercles. A microscopic granulation covers the 

 miliary space (Pf. xxvi, Fig. le). 



The apical disk is small and compact and the perforations of the 

 genital plates distinct (PI. xxvi, Fig. Ig). 



The mouth opening is large, excentric, situated at some distance in 

 front of the center of the base. The anal opening is large, acuminated 

 on the upper margin, and placed in a broad, deep anal sulcus that ex- 

 tends from near the apical disk to the posterior margin (PI. xxvi, 

 Fig. Id). 



Related forms. — JEchinohrissus expcmsus has no points that would 

 closely ally it with any species of this genus hitherto described. 



Locality and geological horizon. — This species is from the Eipley 

 group (upper Cretaceous) of Alabama or Mississippi, but its exact 

 locality is not recorded. 



Collection. — Philadelphia Academy of Natural Sciences. 



EcHiNOBRissus TEXANUS Clark. 



Plate XXVI, Figs. 2a-f. 



Echinoirissus tcxanus Clark, 1891. Jolins Hopkius University Circulars, No. 87, p. 76. 



Determinative characters. — Test ovate, rounded anteriorly, subquad- 

 rate posteriorly; upper surface convex, apex forward of the center; 

 base concave. Ambulacra lanceolate, subpetaloidal. Apical disk for- 

 ward of the center. Mouth opening small, excentric. Anal opening 

 small, oval, in narrow sulcus that begins some distance below the apical 

 disk. 



Dimensions. — Length, f inch; width, | inch; height, -■^%- inch. 



Description. — The single specimen of this species is somewhat dam- 

 aged on the sides, so that tlie ambital outline is not complete. It is 

 ovate in form, broader posteriorly, and subquadrate. The upper sur- 

 face is convex, but more or less compressed. Tlie lower surface is con- 

 cave. 



The ambulacral areas are narrowly lanceolate. The poriferous zones 

 for a short distance from the apical disk are subi)etaloid in form. The 

 Ijosterior ambulacra are much longer than the others, the unpaired 

 ambulacrum being the shortest. The pores of each plate are oval and 

 set at an angle to one another (PI. xxvi. Fig. 2e). 



