9 



vated for the attachment of the column, which is not large, and has a 

 small central perforation; subradials about as wide as high, very 

 tumid, projecting from the body as fine strong nodes ; first radials 

 massive, prominent in the middle, wider than high, bending inward a 

 little between the arms ; arm facets prominent, subcircular, shghtly 

 excavated, with a moderate-sized notch in the upper side, and the 

 lower margin sharply projecting ; anal plate quadrangular (?), nearly 

 as wide where it rests squarely on the subradial as at the top ; suture 

 lines not very distinct ; four or five indistinct, parallel, radiating 

 ridges pass from the middle of each subradial plate to each of the 

 adjacent plates, being more distinct where they cross the suture 

 lines than on the more prominent parts. 



This species may be easily distinguished from others with which it 

 is associated by its radiated surface, very tumid subradial plates, sub- 

 circular arm facets, and its having the true structure of Cyaihocrinus, 

 not approaching Poteiiocrinus, as do some of the Keokuk Limestone 

 species. 



Locality and position, in the Keokuk Limestone, near Burlington, 

 Iowa. — Cabinet of Eev. W. H. Barris. 



Genus Potekiocrinus MUler. 



PoTERiocRiNUS OB-XJNCUS (n. s.) Body cup-shaped, about one 

 third wider than high, upper edge of the calyx much bent in between 

 the arms ; basal plates small, trtmcated for the attachment of the col- 

 umn, which is of medium size, with a small central perforation, bent up 

 at the sides to meet the subradials, which are moderately large, about 

 as wide as high ; first radials larger than the subradials, wider than 

 high, prominent at the base of the arms, giving the calyx a sub-pen- 

 tagonal outline ; arm facets occupying about one-third of the width of 

 the first radials, subcircular, with a broad notch in their upper mar- 

 gins, and a minute perforation in the centre just below the notch, 

 with a fine groove connecting them. Anal plates, two visible in our 

 specimen, one quadrangular, rather small, and situated partly be- 

 neath the first radial of the right posterio-lateral ray. Surface gran- 

 ulose, with a tendency of the granules to form radiating lines. Su- 

 ture lines distinct, with depressions at the angles of the body-plates. 



This species has the aspect and form of Cyatliocrinus, but ap- 

 proaches Poteriocrinus more nearly in the number and oblique posi- 

 tion of the anal plates. It is the first specimen I have observed 

 which shows the subcentral perforation in the arm facet, in rocks of 

 this age, although this peculiarity is not uncommon in species of this 

 genus in rocks of the age of the Upper Helderberg Limestones. 



Locality and position, in the lower division of the Burlington Lime- 

 stone, Burlington, Iowa. — Collection of B,ev. W. H. Barris. 



