78 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



The ambulacra are broad in the petaloidal portion, beyond winch they are narrowed. At 

 the margin they again acquire considerable width but gradually contract beyond, although 

 expanded for a short distance in the phylloidal area near the peristome. At the peristome the 

 final pair of plates is highly attenuated. The pores of the outer rows, in both the petaloidal and 

 phyloidal areas, are in a marked degree elongated. In the intermediate portion of the column 

 they are small and indistinct. 



The interambulacra are more prominent than the ambulacra, which are slightly depressed. 

 The surface is covered with minute tubercles and a microscopic granulation. 



The apical system is large, subcircular, and surrounded by a very prominent flOscelle. The 

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



Related forms. — C. subconicus is closely related to C. subquadratus but is separated from it 

 by its high subcorneal test, more elevated periproct, and shallow anal sulcus. 



Locality. — Dumas, Miss. 



Geologic horizon. — Ripley formation, Upper Cretaceous. 



Collection.— XJ. S. National Museum (20264). 



Cassidulus porrectus Clark. 



Plate XXXII, figures 2a-b; Plate XXXIII, figures la-f. 



Cassidulus porrectus Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 7G. 

 Cassidulus porrectus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 



Cassidulus porrectus Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 72, 73, PL XXXIII, figs, la-b, PI. XXXIV, figs, la-b., 

 PL XXXV, figs. la-d. 



Determinative characters. — Test very large, subcircular, oval, depressed; upper surface con- 

 vex; lower surface concave; broader posteriorly than anteriorly; apex forward of the center. 

 Ambulacra broad. Interambulacra thickly covered with minute tubercles. Apical system 

 small, forward of the center. Peristome large, subcorneal, with prominent floscelle. Periproct 

 supramarginal, in short shallow sulcus. 



Dimensions. — Length 99.6 millimeters; width 97.5 milhmeters; height 44.5 millimeters. 



Description. — This very large Cassidulus has an irregularly oval, depressed test, that is sub- 

 circular in marginal outline. The width is equal to the length but is greatest in the posterior 

 portion, so that the margin appears contracted anteriorly. The apex is some distance forward of 

 the center and slightly flattened. The posterior margin is feebly truncated. 



The ambulacra are wide; the contractions below the petaloidal region and above the phyl- 

 loidal continue for short distances, while the lowest pair of plates in the column bordering the 

 peristome are long and greatly attenuated. The pores of the outer rows are slitlike in form and 

 obliquely placed. 



The interambulacra 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. 

 The apical system is small and is placed forward of the center. 



The peristome is large, subcircular, with very prominent floscelle. The oral lobes project 

 far beyond'the level of the base and are separated by deep ambulacral furrows. 



The periproct is large, oval, and is situated at the head of a short, narrow sulcus. 



Related forms. — C. porrectus is from its size, form, and details of structure readily separated 

 from the other species of Cassidulus described from the American and European Cretaceous. 



Locality. — Euf aula, Ala. 



Geologic horizon. — Ripley formation, Upper Cretaceous. 



Collection.— U. S. National Museum (21890). 



