232 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



obscure ridges or angularities passing out from their margins, and meeting 

 those of adjoining plates -, the median portions perfectly smooth. 



Basals and radials of nearly the same size, both bending abruptly upward, 

 the former to three fourths their length, the others only at the lower ends. 

 Costals one or two ; together about one half the size of the radials, very 

 frequently anchylosed, there being scarcely a specimen with two costals in 

 all fiyQ rays. Of the distichals generally but one plate takes part in the 

 calyx — in very large specimens sometimes two — which is as large as the 

 second costals. Arm openings two to the ray, facing sideways. Arms un- 

 known. Interradial spaces flattened, composed of 1, 2, 3 plates, followed by 

 two others between the arm openings -, the plate between the radials not 

 larger than the interbrachials above ; the two latter separated by a shallow 

 depression, which gives to the arm bases a somewhat lobed appearance, and^ 

 to the tegmen a pentangular outline. Anal side wider, with three plates in 

 the second row ; the plates of the median row forming a vertical ridge of five 

 pieces, which passes up into the tegmen. Ventral disk comparatively large, 

 almost flat; composed of about twenty shghtly convex plates, of which 

 those near the margin are the largest. Anus marginal, on top of a small 

 protuberance. 



Horizon and Locality, — Upper Burlington limestone ; Burlington, Iowa. 



Ty^es in the collection of Wachsmuth and Springer. 



Remarks. — This species resembles the two preceding, but differs essen- 

 tially in the form and proportions of the calyx. In those species the calyx 

 attains its greatest width in the lower half of the dorsal cup, and the teg- 

 men is proportionally narrow ; while in this species the calyx is widest at the 

 bases of the arms. Besides it differs in the construction of the anal side, and 

 in having larger costals and distichals. 



Rhodocrinus tuberculatus W. & Sp. (nov. spec). 



Plate XIIL Figs. 3, 4. 



A very knobby species; somewhat larger than the preceding one. 

 Calyx a little higher than wide; deeply excavated at the bottom; decid- 

 edly bulging at the costals, whence it contracts uniformly to the margin of 

 the ventral disk, where the diameter is fully one third smaller — less than the 

 width at the lower end of the dorsal cup. All plates of the calyx, basals 

 and infrabasals excepted, extended into conspicuous angular tubercles of 

 which those upon the radials are longest and stoutest. 



