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, w^hich 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 

 I5 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- 

 gular ; axial canal very large. 



Horizon and Locality. — Trenton group, near Knoxville, Tenn. 



Ti/;pes in the collection of Wachsmuth and Springer. 



Diabolocrinus vesperalis (White). 

 Plate XL Figs, Ic, d, 



1880. Rhodocrinus vesiieralis — White; Proceed. TJ. S. Museum, Yol. IL, p. 259. 



1883. Rhodocrinus vesperalis — White ; Twelfth Ann. Rep. U. S. Geol. Surv. Terr., by Hayden, p, 129 

 Plate 35, Pigs. 4^, b. 

 Syn. Lyriocrinus sculpUHs — S. A. Miller ; 1882 (not Hall 1851), Cincin. Journ. Nat. Hist., Vol. 



v., p. 117, Plate 3, Pigs. 6«, b. 

 Syn. Lyriocrinus scuIptus—S. A. Miller; ibid, (private ed., Explanation of plate). 

 Syn. Archaocrinus sculpfus — 'W. and Sp. 1885 ; Revision Palaeocr., Part III., pp. 96-98. 

 Syn. ArclifBOcrinus sculptus — %. A. Miller, 1889 ; North Amer. Geol. and Palaont., 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 striae. 



Infrabasals invisible beyond the column. Basals large, elongate, the prox- 



