Carboniferous Rocks of the Mississippi Valley. 323 



from four to six plates, the first one much smaller than the 

 first radial, varying from pentagonal to heptagonal, sup- 

 •porting two in the second and two in the third range, with 

 sometimes a small plate above. The anal series does not 

 differ from the interradial so far as can be determined. 



Arms two from each ray, and bifurcating at more than 

 one third their length from the base ; above this they con- 

 tinue simple ; composed of a single series of short plates, 

 alternately thicker and thinner on opposite margins ; the 

 thin edge is frequently so attenuate as to allow the plates 

 above and below to touch. The tentacula arise from the 

 longest sides, and are composed of comparatively long, 

 cylindrical joints, each equal in height to two arm joints. 

 Plates of the body ornamented by sharp, angular nodes 

 and spines, which are united across the sutures by ridges ; 

 those of the sub-radial and first radial plates are equal in 

 length to the greatest diameter of the plate. The nodes 

 of the sub-radials are directed downwards ; those of the 

 first radials extend horizontally. The ridges which pass 

 from the sub-radials to the first radials are strongest and 

 most prominent, surrounding the body with a series of V 

 shaped ornaments, in the upper part of which the first 

 interradial plate, with its less conspicuous ridges, forms a 

 stellate centre. Column small, composed of alternating 

 larger and smaller joints. 



This small and handsome species is easily distinguished 

 by the surface markings. The lower part of the calyx 

 has a strong resemblance to specimens of the genus Tre- 

 matocrinns ; but the arms rise directly from the rays, and 

 are entirely separated from the adjacent rays (arms) by the 

 interradial and anal spaces, which extend above the arm 

 bases and are united with the dome. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collection of Rev. W. H. Bar- 

 ris. 



