PALAEONTOLOGY OF IOWA. 581 



of proboscis to origin of arms about two-thirds as great as 

 from origin of arms to base of calyx ; base concave for the 

 reception of the column. Basal plates projecting over the 

 column in a thin rim, and deeply indented at the line of 

 junction : plates above the rim short. First radial plates 

 hexagonal, about two-thirds as long as wide. Second radials 

 hexagonal, having the upper lateral angles shortly truncated 

 by the second interradial plates, nearly twice as wide as 

 long. Third radials pentagonal, supporting on each upper 

 oblique side a pentagonal supraradial plate, and each one of 

 these two other plates, the outer ones being truncate above 

 and supporting a single brachial plate ; while the inner ones 

 are wedgeform above, and support on one side a brachial 

 plate and on the other a third supraradial plate, giving four 

 brachial plates to each first supraradial ; the outer ones sup- 

 porting a second brachial plate, thus giving four arms or 

 eight arms from each ray. First interradial plate hexagonal, 

 supporting two smaller hexagonal plates, which on their 

 principal upper sides support the first supraradial plates. A 

 single third interradial plate rests above and between the 

 second interradials, supporting on its upper sides the outer 

 brachial plates of adjacent rays. 



ARMS composed of a double series of short broad plates to 

 the number of forty in the space of one inch, very obtusely 

 wedgeform at the inner margins. Plates of the calyx all 

 marked by strong radiating angular ridges, which meet in 

 an angular node on the centre, or form a transverse ridge. 

 Plates of the summit subangularly tuberculous : proboscis 

 composed of numerous short transverse plates, with sharp 

 projecting edges. Column near the body composed of alter- 

 nating thicker and thinner joints, and, at a greater distance 

 from the body, of three different sets of joints which are 

 deeply striated upon the articulating surfaces. 



Fig. 19. View of anterior side of specimen, showing the body with part of the column 

 and proboscis, with a portion of the arms of the opposite side. 



