PLATYCRINID^. 733 



interradial and basi-radial sutures, and from the latter to the column. Suture 

 lines faintly grooved, except the interbasal ones, which are obsolete. Ventral 

 disk low hemispherical, the plates convex. 



Basal disk a little concave, large, decagonal in outline, the faces meeting 

 the radials being more or less distinctly angular. Column facet small, cir- 

 cular, shghtly excavated, and surrounded by a faint ridge; the axial canal 

 large and obscurely pentagonal. Radials at their widest place twice as 

 wide as long. Costals extremely small. Distichals large, their outer lateral 

 faces longer than those meeting the costals, their lower faces resting upon the 

 radials. Interradial plate large, placed vertically ; the extreme upper end 

 slightly incurving; its lower faces rest between two of the radials, the lateral 

 ones between the second costals, and the three upper support three interam- 

 bulacrals, which are followed by two others in the next row, and these by 

 the orals. Orals quite asymmetrical and small. Ambulacra exposed at 

 the disk, the covering pieces very regularly arranged; composed of rather 

 short, transverse pieces alternately disposed. 



Horizon and Locality. —Niagara group; Decatur Co., West. Tennessee. 



Types in the collection of Wachsmuth and Springer. 



Remarks. — 1\\\'& species differs from M. tenneseensis in the very much 

 larger basal disk, which in this species is generally decagonal. The differ- 

 ences in the ventral disk are also quite marked, the ambulacral plates 

 especially being much larger. 



Marsupiocrinus tentaculatus* (Hall). 

 Plate LXXV. Figs. 19a, b. 



1858. riatycrinus ieniaculatus — S.lia.; Pala:ont. N. York, Vol. III., p. 116, Plate 5, FiVs. 1-4. 

 1881. Marsupiocrinus tentaculatus — ^i . and Sp. ; Revision, Part II., p. 65 (Proceed." Acad Nat Sci 

 Phila., p. 239). 



A much smaller species than the preceding one, and having twice as 

 many arms. Dorsal cup short, bowl-shaped, shghtly lobed at the top. 

 Surface of plates ornamented by radiating ridges, of which seven or eight 

 proceed from the lower edge of the costals to the basi-radial and interradial 

 sutures, and to the basals, where they end in a circular rim surrounding the 

 column facet. 



* The specific name has reference to the large pinnnles, which by some of the earlier writers were 

 called tentacles. 



