CRETACEOUS ECHINODERMATA. 79 



Cassidulus stantoni Clark. 



Plate XXXIII, figures 2a-d. 



Cassidulus stantoni Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 76. 

 Cassidulus stantoni Clark, 1S93, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 

 Cassidulus stantoni Clark, 1893, U. S. Geol. Survey Bull. 97, p. 73, PL XXXV, figs. 2a-d. 



Determinative characters. — Test small, subovate, elevated; upper surface convex, lower 

 surface concave; apex forward of the center. Ambulacra very narrow. Apical system small, 

 forward of the center. Peristome small, with floscelle. Periproct high above margin, in long, 

 narrow, and deep sulcus. 



Dimensions. — Length 15 millimeters; width 14 millimeters; height 6.5 millimeters. 



Description. — This minute Cassidulus has a subovate test, an elevated convex upper sur- 

 face, and a concave lower surface. It is broader posteriorly than anteriorly, and its posterior 

 margin is truncated. The apex is situated slightly anterior to the center of the upper surface. 



The ambulacra are very narrow. The petaloidal portion but slightly exceeds the remainder 

 in width, which is nearly equal throughout. The phylloidal region is feebly outlined. 



The interambulacra are broad, but the poor state of preservation of the specimens renders 

 it impossible to determine all the details of structure. 



The apical system is small and forward of the center, but not sufficiently well preserved 

 to distinguish the individual plates. The peristome is small and surrounded by a feeble flos- 

 celle. The periproct is round and situated high above the margin, at the head of a narrow deep 

 sulcus. 



Related forms. — C. stantoni is quite unlike any other representative of this genus from Ameri- 

 can strata and can not be readily associated with any European species. 



Locality. — Muddy Creek, Huerfano County, Colo. 



Geologic horizon. — Colorado group, Upper Cretaceous. 



Collection. — U. S. National Museum (20260). 



Cassidulus intermedius Slocum. 



Plate XXXIV, figures la-f. 



Cassidulus intermedius Slocum, 1909, Field Mus. Nat. Hist. Pub. 134, Geol. ser., vol. 4, No. 1, pp. 6, 7, PI. I. figs. 1-6. 



Determinative characters. — Test oval, depressed, rounded anteriorly, slightly rostrated pos- 

 teriorly. Apex excentric anteriorly. Ambulacra narrow. Peristome large, slightly in front 

 of center of ventral surface. Periproct on upper surface, about one-thud of the distance from 

 the apex to the margin, in broad deep sulcus. 



Dimensions. — Type specimen: Length 25.6 millimeters; width 22.7 millimeters; height 9.6 

 millimeters. 



Slocum saj's: 



Description. — Test oval, greatest width posterior to the center; rounded anteriorly, slightly rostrated posteriorly; 

 dorsal surface convex, apex excentric anteriorly and inflated, sides declining about equally towards the margins which 

 are slightly inflated ; the peristomal concavity occupying more than half of the central surface. Ambulacra! areas nar- 

 row and flush, poriferous zones subpetaloidal on the upper part of the dorsal surface to a point varying in the different 

 areas from about one- third to nearly one-half the distance from the margin to the apical system; the zones are then con- 

 tracted and continue as narrow bands over the margin to the vicinity of the peristome, where they abruptly widen, 

 and gain narrow to the peristome forming a floscelle. The pores are distant and paired on the petaloid portion and in 

 the floscelle; on the narrow connecting portions they are single, small and indistinct. In the petaloid areas the pores 

 of the outer rows are slitlike, those of the inner row round and smaller; each pair is connected by a groove. Inter- 

 ambulacral areas composed of large plates, the plates nearest the peristome in each area inflated forming the bourrelets. 

 Dorsal surface covered with small crowded tubercles with slightly sunken areoles, the tubercles on the ventral surface 

 rapidly increasing in size and distance apart as they approach the peristome. A wide, longitudinal median band extends 

 from near the anterior margin through the floscelle to the posterior margin. This band is without tubercles and the 

 surface is smooth except where it passes through the floscelle. The apical system in the type specimen is too incomplete 

 for detailed description, but appears similar to other species of this genus. The peristome is situated slightly in front of 

 the center of the ventral surface, pentagonal, surrounded by a well-marked floscelle, the bourrelets large and prominent , 



