Oct., 1907. 



New Crinoids — Slocom. 



299 



Locality : The species is represented by a single individual collected 

 by the writer in the fall of 1905, in the Niagaran limestone in the spoil 

 heaps along the Chicago Drainage Canal, about one mile east of 

 Lemont, Illinois. 



¥% 



Family THYSANOCRINID^. 



THYSANOCRINUS Hall. 



Weller's description* of this genus is as follows: — 

 "Calyx subglobose, urn or bell-shaped, the rays marked by more or 

 less conspicuous ridges; the surface of the plates smooth, or variously 

 ornamented. Infrabasals five small, barely extending beyond the 

 column, or entirely hidden by 

 it. Basals five, four of them 

 equal and angular above ; the 

 fifth truncated and support- 

 ing a large anal plate. Radi- 

 als considerably larger than 

 the costals, their proximal 

 sides distinctly angular, the 

 lateral faces comparatively 

 short. Costals two. Distich- 

 als two or three in each series. 

 In some cases palmers are 

 also present, the axillary dis- 

 tichal giving rise on the inter- 

 radial side to an armlet for 

 the most part included in the 



calyx and on the other side of the main arm. Four of the first inter- 

 brachials large, angular below, resting upon the sloping upper corners 

 of the two radials and against the costals; two plates in the second 

 row, often followed by smaller ones above which connect with the 

 plates of the disc. The anal side considerably wider, the first plate 

 large, hexagonal, resting upon the truncated posterior basal, three 

 plates in the second row and smaller ones above. In some species 

 an uninterrupted row of anal plates extends to the anal opening. 

 Interdistichals generally represented and rather large. Column 

 round or obtusely pentangular." 



Thysanocrinus campanulatus sp. nov. Plate LXXXV, Figs. 20-23. 

 The calyx is bell-shaped, expanding very rapidly above the top of 

 * Bull. IV, Pt. I, Nat. Hist. Surv., Chicago Acad. Sci., p. 70. 



Fig. 11. Diagram of Thysanocrinus. 



