704 THE CRINOIDEA CAMERATA OF NORTH AMERICA, 



distichals. Arms from six to eight to tlie raj, given off alternately from 

 opposite sides ; comparatively thin, and gradually tapering to a sharp point. 

 They are even in the most adult specimens uniserial at the proximal end, 

 being composed of cuneate pieces to the fifth or sixth plate above the bifur- 

 cation. The interlocking of the plates evidently took place in this species at 

 a late period in the growth of the individual, for in a specimen in which the 

 crown measures 22 mm., they are still uniserial to the very tips. The joints 

 are rather long, and their surface is covered by small granules, so minute 

 that they are visible only with the help of a magnifier. The edges of ap- 

 posed faces, from the costals up, are distinctly serrated, and the median por- 

 tions of the lower brachials are provided with a small transverse ridge. 

 Pinnules closely arranged in the adult, separated in young specimens ; the 

 joints very long. 



Ventral disk hemispherical, slightly bulging at the sides, the plates tuber- 

 culous, large, and nearly of equal size. In some specimens the orals are some- 

 what larger, and the posterior one sometimes bears two or three nodes 

 instead of one. The covering plates are arranged in rows, and pass out 

 from the orals. Interambulacral pieces apparently four. The anus is located 

 low down at the side, and is very rarely seen, being most generally covered 

 by a Capuh. 



Stem moderately large, circular at the extreme upper end, then turning 

 to elliptical. The joints gradually increase in length, until they are at the ■ 

 lower end of the stem three times as long as at the upper. The outer mar- 

 gin of the upper ones is surrounded by a row of small nodes placed at equal 

 distances, but on approaching the lateral appendages there ai-e but two, 

 which are larger and placed at the long diameter of the joints. Length of 

 the stem not exceeding 25 cm., but generally shorter, terminating in a sharp 

 point. Lateral cirri short and circular. 



Horizon and Locality. — Keokuk group. Found in large quantities and 

 excellent preservation at Crawfordsville, Ind. ; rare at Keokuk, Iowa. 



Ty2Je in the Illinois State collection, Springfield. 



