Carboniferous Rocks of tlie Mississippi Valley. 295 



union a pentagon with salient angles, slightly convex below. 

 Sub-radial plates proportionally very large, hexagonal and 

 heptagonal, length and width nearly equal, convex in the 

 centimes, with a somewhat conspicuous articulating facet 

 for the attachment of the arms, occupying nearly two 

 thirds the width of the plate, and somewhat concave. 

 Anal plates unknown ; but the large sub-radial plate is 

 truncated on the top for the reception of a single large 

 anal plate. Sub-brachial plates one or two to each ray, 

 broad and strong, but varying in the different rays ; the 

 upper ones angular above, and supporting on then- upper 

 sides the first arm plates. 



Arms composed of a single series of plates, bifurcating 

 two or three times, rapidly diminishing in size at each bi- 

 furcation ; the first division is on the first or second plate 

 above the cuneate sub-brachial plate, the next division on 

 the second plate above the first bifurcation ; the interven- 

 ing plates are sometimes very short, and give a very 

 crowded appearance to the arms at the bifurcations. Col- 

 umn round, of medium strength, composed near the body 

 of thin plates, alternating in size and thickness. 



This species has the general form of C. rottindatns, 

 (Iowa Geol. Rep. pi. 9, fig. 7,) but differs in the greater 

 convexity of the body plates, the proportionally large sub- 

 radial plates, and the rapidly diminishing arms. (This 

 last feature may be in part due to injury sustained in an 

 early stage of growth.) 



Geological formation and locality. Keokuk limestone, 

 Keokuk, Iowa. Collection of C. A. White. 



Cyathocrinus macropleurns (n. s.). Body sub-turbinate 

 to the top of the sub-radial plates, whence it rises more 

 abruptly to the middle of the first radial plates, abruptly 

 contracted above, truncate at base. Basal plates short, 

 pentangular, much wider than high, forming when united 

 a low cup, with an undulating margin and five salient 



