PLATYCRINID&. Io3 
interradial and basi-radial sutures, and from the Jatter 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, slightly 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. 
fiemarks.— This species differs from IM. 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* (Hatz). 
Plate LXXV. Figs. 19a, b. 
1858. Platyerinus tentaculatus —Hati; Paleont. N. York, Vol. III., p- 116, Plate 5, Figs. 1-4. 
1881. Marsupiocrinus tentaculatus —W. and Sp.; Revision, Part IL., 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, slightly 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 pinnules, which by some of the earlier writers were 
called tentacles. 
