CBETACEOUS ECHINODEKMATA. 39 



Family MARSUPITIDJE. 



Genus MAR STTPITE S Miller. 

 Maesupites americanus Springer. 

 Plate VII, figures 2a, 2b, 3. 

 Marsupites americanus Springer, 1911, Mus. Comp. Zool. Mem., vol. 25, No. 3, pp. 158-161, PI. VI, figs. 4a, 4b, 5. 

 Springer describes the species as f ollows : 



Determinative characters. — Calyx globose, wider than high; widest about middle of basal, contracting toward the 

 arm bases. Centrale larger than infrabasals. * * * Radial facets shallow, facing almost vertically; filling about 

 half the distal face of radial, and having a straight muscular- articulation. Primibrachs 2 ; succeeding brachials to the 

 number of seven in the longest arm preserved wide and very short, with an alternating cuneiform arrangement and an 

 indication of syzygies between Br3 and 4; ventral groove broad and shallow. A good-sized triangular interbrachial 

 plate, having straight sides and apparently joined to the brachials by suture, fills the space between the arm bases. All 

 plates very thin, and covered with moderately fine radiating strife crossing the sutures and converging at the centers- 

 a strong ridge runs upward from the center of the basals, two meeting at each radial facet. Further structures unknown. 



Dimensions. — Centrale: Diameter of pentagon 18 millimeters; IBB 17 millimeters high by 17.5 wide; BB 18 milli- 

 meters high by 18 wide; RE. 11 millimeters high by 14 wide; radial facets 6 millimeters wide. In a large fragment the 

 centrale is 25 millimeters wide. 



Description. — The general outline and surface ornament of this species are not different from what may be seen 

 •among specimens of M. testudinarius of the English chalk from Sussex and other places. These vary from coarse to fine 

 stria? and with such a thin, pliant calyx the contour of the fossil is largely a matter of pressure in its deposition. Meas- 

 urements of plates shows no substantial difference between the two, an average of five specimens of the English species 

 being as follows: Centrale, 19.1 millimeters wide; IBB, 19.6 millimeters high by 19.5 wide; BB, 19.6 millimeters hi°-h 

 by 20.1 wide; RR, 12.6 millimeters high by 15.7 wide; R, facets 8 millimeters wide. The only real difference observ- 

 able in the parts preserved is that in our species the brachials are shorter and wider than in M. testudinarius; and if we 

 had enough specimens with brachials attached to get an average, this might disappear. The calyx figured is smaller 

 than the English species usually appears, but the other fragmentary specimen has plates fully as large as that. The 

 species is rare and has only been found at the type locality. 



Locality. — Plymouth Bluff, Miss. 



Geologic horizon. — Tombigbee sand member of the Eutaw formation, Upper Cretaceous. 



Collection. — Collection of Frederick Braun. 



Order FLEXIBILIA. 



Suborder PINNATA. 



Family BOURGUETICRINID;E. 



Genus RHIZOCBINTJS M. Sars. 



Rhizocrintts alabamensis (De Loriol). 



Plate VII, figures 4a-c. 



Bourgueticrinus alabamensis De Loriol, 1882, Cincinnati Soc. Nat. Hist. Jour., vol. 5, p. 118, PI. V, figs. 1, la, lb. 

 Rhizocrinus alabamensis Carpenter, 1884, Challenger Repts., vol. 11, pt. 2, p. 257. 

 Bourgueticrinus alabamensis Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Bourgueticrinus alabamensis Clark, 1893, U. S. Geol. Survey Bull. 97, p. 25, PI. Ill, figs. la-c. 



Description. — As it has been impossible for the writer to obtain possession of the type of this 

 species the description of De Loriol, as translated by S. A. Miller, is given verbatim: 



This species is as yet known only by the basal cone which supports the calyx, and which is composed of several 

 enlarging segments of the column surmounted by the basal plates. The height of the inverted cone is 5 millimeters; 

 the diameter of the basal plate is 3A millimeters; and that of the inferior segment of the column is 3 millimeters in its 

 major axis. Its form is faintly swollen in the middle; the surface is smooth. The sutures are very indistinct, and it is 

 a difficult matter to determine what was the height of the basal plate. The superior face of the cone carries five slender 

 and compatively elevated radiating ridges, which bound five deep depressions in which the basal pieces of the calyx 

 were lodged ; in the center an enlargement of the central canal constitutes the bottom of the calyx cavity. The articu- 

 lar face of the lower joint of the column forming the inferior end of the cone is elliptical, but the length of its major 

 axis does not, however, much exceed that of its minor axis. It is slightly concave and encircled by a feeble rim along 



