532 PALEONTOLOGY OF ILLINOIS. 



generally showing a slight disposition to become a little 

 zigzag, and, at least some of them, throwing off alternately 

 on each side a series of smaller secondary armlets, exactly 

 as they are themselves given off by the arms. Secondary 

 armlets shoAviiig a slight zigzag appearance, from the 

 greater thickness and prominence of every second piece 

 on opposite sides, so as to appear as if they may give off a 

 tertiary series of armlets or pinnulse, though the specimen 

 does not show these, if they exist. Column very stout, 

 nearly round, and composed, at least for about three inches 

 or more below the base, of alternating thin, and somewhat 

 thicker pieces, the latter of which project outward a little 

 beyond the others, and show a slight disposition to become 

 nodular, or irregularly thickened on the edges. Internal 

 cavity large, or equaling about half the diameter of the col- 

 umn itself, and showing an obtusely sub-pentagonal trans- 

 verse section, the angles being rounded. Longitudinal 

 sutures dividing the column into five sections, partly 

 anchylosed, but still distinctly visible. 



Hight of body, about 1 inch; breadth, about 1.70 inches; 

 length of arms, 3.80 inches; thickness of do. at the base, 

 0.40 inch; thickness of column near base, 0.60 inch. 



This fine, large species seeins to be most nearly allied to B. Thoma', 

 (=Gyathocrinus Thomce, Hall,) from the Warsaw Limestone, but (lifters 

 in having the impressions at the corners of its body plates, and the 

 ridges between the same, greatly more strongly defined, and its arms 

 much stouter and more rounded below. Its column is also proportion- 

 ally stouter, and has a more obtusely pentagonal internal cavity. The 

 typical specimens of B. Tliomce, Avhich are now before us, are not in a 

 condition to show the arms all the way up, but as far as they can be 

 seen, they are proportionally more slender, and we can scarcely doubt 

 but that they will show other corresponding differences in the details of 

 their structure, when better specimens can be compared. We have 

 ascertained, however, that the arm pieces of the typical specimens of 

 B. Tkoma' have on their sides the same kind of little angular projections 

 seen on our species, which character was not mentioned in the descrip- 

 tion of Prof. HALL'S species. 



