72 MESOZOIC ECHINODERMATA OF THE UNITED STATES. [boll. 97. 



plates and five ocular- plates. The fifth genital is apparently obsolete 

 (PL XXXII, Fig. IJc). 



The mouth opening is large, subcircular, and surrounded by a very 

 prominent floscelle (PI. xxxii, Fig. Ih). The anal opening is large, 

 circular, and is situated high above the margin in a shallow sulcus. 



Belated forms. — Cassidulus subconicus is closely related to G. suh- 

 quadratus, but is separated from it by its high subcorneal test, more 

 elevated anal opening, and shallow anal sulcus. 



Locality and geological horizon. — Like the preceding species, Cassidu- 

 lus suhconicus is from the Kipley group (upper Cretaceous) of Missis- 

 sippi. 



Collection. — U. S. National Museum. 



Cassidulus porrectus Clark. 



Plate xxxiii. Figs, la-h-, Plate xxxiv. Figs, la-h; Plate xxxv, 



Figs, la^d. 



Cassidulus porrectus Clark, 1891. Johns Hopkins University Circulars, No. 87, p. 76. 



Determinative characters. — Test very large, subcircular, oval, de- 

 pressed; upper surface convex; lower surface concave; broader pos- 

 teriorly than anteriorly; apex forward of the center. Ambulacra broad. 

 Interambulacra thickly covered with minute tubercles. Apical disk 

 small, forward of the center. Mouth opening large, subconical, with 

 prominent floscelle. Anal opening supra-marginal, in short shallow 

 sulcus. 



Dimensions. — Length, 4 inches; width, 4 inches; height, 2 inches. 



Description. — This very large Cassidulus, with one exception the 

 largest Echinoid in the American Mesozoic, has an irregularly oval, 

 depressed test, that is subcircular in marginal outline. The breadth is 

 equal to the length, but is greatest in the posterior portion, so that the 

 margin appears contracted anteriorly. The apex is some distance for- 

 ward of the center and slightly flattened. The posterior margin is 

 feebly truncated. 



The ambulacral areas are wide; the contractions below the petaloidal 

 region and above the phylloidal continue for short distances, while the 

 lowest pair of plates in the column bordering the mouth opening are 

 long and greatly attenuated (PI. xxxv. Fig. la). The pores of the 

 outer rows are slit-like in form and obliquely placed (PI. xxxv, Figs. 

 16, Ic). 



The interambulacral areas are prominent; the plates are covered with 

 numerous small tubercles, with depressed areolas, which are larger and 

 more prominent on the under than the upper surface (PI. xxxiii. Fig. 

 Id!). The apical disk is small and is placed forward of the center. 



The mouth opening is large, subcircular, with very prominent flos- 

 celle. The oral lobes project far beyond the level of the base and are 

 separated by deep ambulacral furrows (PI. xxxiv. Fig. la). 



