Carboniferous Rocks of the Mississippi Valley. 313 



folds, extending from the centre to the upper sloping mar- 

 gins, those of the two adjacent plates converging, and 

 meeting corresponding elevations on the two lateral slop- 

 ing margins of the first radial plates ; and these, uniting 

 just below the upper truncate margin of the plate, give it 

 a strongly thickened upper side, upon which the second 

 radial rests ; less conspicuous folds or elevations mark the 

 other plates; and the entire surface is marked by sharp, 

 slender, radiating strite. 



The body of this species might be mistaken for Cyatho- 

 crinus rhombifer of Owen, or Cyat/tocrinus sculptilis of 

 Hall, (Supp. Geol. Rep. of Iowa,) but the calyx is less 

 spreading, the plates less robust, and the surface different, 

 while the sub-radial plates are proportionally much larger 

 and longer, and the first radial plates proportionally small- 

 er. Above this point, the structure and form of parts indi- 

 cate the generic distinction. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collection of C. A. White. 



Sca.phio crinus unicus (n. s.). Body shallow cup-shaped, 

 broad, with moderately spreading sides, and deeply im- 

 pressed base. Basal plates occupying the bottom of the 

 basal cavity, and mostly concealed by the large column. 

 Sub-radials of moderate size, three hexagonal, and two on 

 the anal side heptagonal ; their lower ends form the sides 

 of the basal cavity. First radials larger than the sub- 

 radials, nearly twice as wide as high, sub-pentangular, the 

 upper portion somewhat projecting ; articulating facet con- 

 cave. Second radial plates on the anterior ray sub-quad- 

 rangular, longer on one side than on the other, supporting 

 a single arm, which is simple throughout its entire length ; 

 those of the other rays pentangular, once and a half as 

 wide as high, rather sharply angular above, slightly con- 

 stricted in the middle, supporting on each upper sloping 

 edge an arm, which divides into three or rarely four 



JOURNAL B. S. N. H. 40 



