202 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
central, large, and extended into a heavy, short spine; the other four orals 
proportionally small and almost flat. Radial dome plates represented by 
plates of a first and second order, those of the latter by two or three plates 
to each division, alternately arranged; all large and spine-bearing. The 
spines near the outer margins of the disk project obliquely outward, and are 
visible from a dorsal view of the calyx. Interambulacral plates numerous, of 
the size of the smaller orals, and irregularly arranged. Anus excentric, at 
the top of a large ovoid protuberance, rising conspicuously above the general 
plane of the disk. 
Horizon and Locality. — Niagara group; St. Paul, Shelby Co., Ind. 
Type in the collection of Wachsmuth and Springer. 
IDIOCRINUS W. and Srp. (nov. gen.). 
(id:0s, peculiar ; xpivor, a lily). 
1892. W. and Spr.; Am. Geologist, Vol. X. (September), p. 135. 
Syn. Gazacrinus S. A. Miter (October 26, 1892); Adv. Sheets, 18th Rep. Geol. Sury. Indiana, 
p- 49. 
Infrabasals apparently five, extremely small, placed at the bottom of 
a more or less deep concavity, and completely hidden by the column. Basals 
five, very large; the posterior one truncated by the anal plate. Radials quite 
large ; three of them heptagonal, the two adjoining the anal side hexagonal. 
Costals two, very short; the first quadrangular; the second pentangular, 
the upper angle rather obtuse. Distichals two in the calyx; short. Inter- 
radial areas at all sides composed of a single large plate, which rises to the 
top of the dorsal cup ; that of the anal side resting upon the basals, the four 
others upon the sloping upper faces of the radials. Ventral disk quite vari- 
able in form; covered by a large, probably anchylosed oral pyramid. The 
ambulacra tegminal; the interambulacral spaces formed of single plates, 
of which the posterior one is perforated by the anus, which is excentric. 
Arms and column unknown. 
Type. — Idiocrinus elongatus. 
Distribution. — So far as known, restricted to the Niagara group of 
America. 
Remarks. — This genus differs from all other dicyclic Camerata in having 
a single plate in the anal area, in its central, undivided oral pyramid, and in 
having but one interambulacral plate to each side of the disk. 
