80 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



the phyllodes very narrow as they reach the peristome and situated in grooves. The periproct is elongated longitudi- 

 nally and situated on the dorsal surface about one-third the distance from the posterior margin to the apex in a deep 

 groove. 



Related forms. — In general form this species resembles C. xquoreus, but is not so high in proportion to its length, the 

 periproct is somewhat higher, the pores in the outer rows of the petaloid portions are slitlike instead of round, and the 

 expansions of the phyllodes are wider. C. intermedins resembles C. micrococcus in the slitlike pores of the outer rows 

 of the petaloid areas and in the expansion of the phyllodes, but the position of the pores in these expansions is more 

 like those of C. xquoreus. The position of the periproct is midway between that of C. micrococcus and C. xquoreus, the 

 size and shape of the test is quite unlike C. micrococcus and the extension of the longitudinal median band in front of 

 the peristome on the ventral surface does not appear, from the description and figures, to occur in either of the other 

 species. The name adopted for this species refers to the characters intermediate between C. xquoreus and C. micrococ- 

 cus which the sjiecies exhibits. 



Locality. — Near the southern edge of the village of Pontotoc (Slocum), Miss. 

 Geologic horizon. — Ripley formation, Upper Cretaceous. 

 Collection. — Field Museum of Natural History (P 10346). 



Cassidulus hemispherictjs Slocum. 



Plate XXXIV, figures 2a-c. 



Cassidulus hemisphericus Slocum, 1909, Field Mus. Nat. Hist. Pub. 134, Geol. ser., vol. 4, Pc . 1, pp. 7, 8, PI. I, figs. 7-9. 



Determinative characters. — Test subhemispherical, elevated, margins angular, lower surface 

 flat. Ambulacra wide. Peristome nearly central. Periproct supramarginal. 



Dimensions. — Type specimen: Length 34.7 millimeters; width 26.7 mill im eters; height 

 19.5 millimeters. Allowing for the lateral crushing it is probable that the length and width 

 were originally about 32 millimeters and 29 millimeters, respectively. 



Description. — Slocum says : 

 Test subhemispherical with its transverse diameter somewhat shorter than the longitudinal, sides arcuate, margins 

 angular, ventral surface flat or nearly so. Ambulacral areas wide, subpetaloidal on the top of the dorsal surface, not 

 closed distally, petals subequal in length, extending about halfway from the apex to the margin, slightly convex; from 

 the distal end of the petals the ambulacral areas are continued as a band which gradually increased in width from the 

 petal to the margin, most of the way being wider than the petal. On the ventral surface the bands slightly narrow to 

 the floscelle. The floscelle is not well preserved in the type specimen, but enough is preserved to determine that the 

 bourrelets are prominent and that the phyllodes are in grooves. The apical system is central but the form of the various 

 plates of which it is composed can not be determined. The interambulacral areas are about equal in size. They form 

 an acute angle near the apex and rapidly expand to the margin, the plates being comparatively large. All the plates 

 of the dorsal surface, with the exception of those of the petals, are marked by prominent lines subparallel to the edge 

 of the plates. These lines are farther apart on the lateral edges than on the proximal and distal edges. They appear 

 to be lines of growth. The middle portion of the plates within this series of lines is inflated, so that in the small plates 

 of the interambulacrai areas, near the apex, the centers of the plates appear as prominent nodes. These middle portions 

 of the plates are free from tubercles, but the parts of the plates covered by the parallel lines and the plates of the petals 

 are covered with minute tubercles closely crowded together. The lines are much less prominent on the plates of the 

 ventral surface and the tubercles are larger, with slightly sunken areoles, and more evenly distributed over the surface, 

 except on the longitudinal median band, which extends from the peristome to the posterior margin. The peristome is 

 situated at the center of the ventral surface, surrounded by a floscelle, the bourrelets are prominent, and the phyllodes 

 are depressed and contracted into narrow grooves where they reach the peristome. The periproct is supramarginal, 

 but its form and exact position are unknown, because that portion of the posterior interambulacral area near the margin 

 is missing. 



Locality. — The "white gullies" on the Patterson farm, about 3 miles south of Pontotoc, 

 Miss. 



Geologic horizon. — Ripley formation, Upper Cretaceous. 

 Collection.— Field Museum of Natural History (P 10347). 



Cassidultjs conoideus Clark, n. sp. 

 Plate XXVII, figures 3a-d. 



Determinative characters. — Test moderate, nearly circular, inflated above, flat below. 

 Apical system excentric anteriorly. Ambulacra nearly similar, subpetaloid. Peristome excen- 

 tric forward. Periproct supramarginal in poorly defined groove. 



Dimensions. — Length 31.5 millimeters; width c52 millimeters; height 2S millimeters. 



