RHODOCRINID. 251 
Infrabasals completely hidden by the top stem joint. Basals large, elon- 
gate, barely seen in a side view, longitudinally grooved at the median line, 
which gives to the cavity a decidedly pentangular outline; the angles of the 
upper face truncated for the reception of supplementary pieces, which in this 
species are not only constantly represented but quite regular in their arrange- 
ment. Costals less than half the size of the radials. Distichals still smaller 
and free above the first. Arm openings in pairs; elongate. Interradials 
1, 2, 3 in the dorsal cup; the first, which is nearly as large as the basals, 
surrounded variously by from two to four supplementary pieces, two of them 
abutting against the radials and basals, and two against the radials and first 
costals. These plates vary greatly in size, being in some specimens very 
minute, while they are comparatively large in others. In very large speci- 
mens, when completely developed, the first regular interradial is surrounded 
by six plates — including the two regular interradials of the second row — 
and by seven plates at the anal side. In cases in which the supplementary 
pieces are small and imperfectly developed, the first interradials touch the 
radials and basals. Tegmen composed of rather large plates without any 
regularity in their arrangement; the interradial portions depressed, those 
concealing the ambulacra quite prominent. Column small, obtusely pentan- 
cular; axial canal very large. 
Horizon and Locality. — Trenton group, near Knoxville, Tenn, 
Types in the collection of Wachsmuth and Springer. 
Diabolocrinus vesperalis (Wut). 
Plate XI. Figs. Ic, d. 
1880. Rhodocrinus vesperalis — Wuitn; Proceed. U. 8. Museum, Vol. II., p. 259. 
1883. Rhodocrinus vesperalis —Wuite; Twelfth Ann. Rep. U. 8. Geol. Surv. Terr., by Hayden, p. 129, 
Plate 35, Figs. 4a, 6. 
Syn. Lyriocrinus sculptilis —S. A. Mituer 3 1882 (not Hall 1851), Cincin. Journ. Nat. Hist., Vol. 
V., p. 117, Plate 3, Figs. 6a, d. 
Syn. Lyriocrinus sculptus — 8. A. MitiER; ibid. (private ed., Explanation of plate). 
Syn. Archeocrinus sculptus —W. and Sp. 1885; Revision Paleoer., Part III., pp. 96-98. 
Syn. Archeocrinus sculptus —S. A. MituEr, 1889; North Amer. Geol. and Palewont., p. 225. 
Calyx depressed subglobose, pentangular across the arm bases; the basals 
to one third their length forming a funnel-shaped concavity, of which the 
infrabasals form the bottom part. Plates but very slightly convex, densely 
covered by wrinkles or indistinct strix. 
Infrabasals invisible beyond the column. Basals large, elongate, the prox- 
