194 PALAEONTOLOGY OF ILLINOIS. 



Radials once and a half as wide as high, and about of equal 

 size, but differing somewhat in form although all are penta- 

 gonal; the two facing the anal piece, owing to the greater 

 length of the posterior basal, irregular. The upper face of the 

 radials, throughout the full width of the plates, truncated and 

 slightly concave. Brachials one, of the same height as the radials ; 

 pentangular, but subtrigonal in outline, upper angles sharply 

 pointed; line of articulation toward radials and also first arm 

 plates widely gaping. 



Arms ten, long, moderately stout, gradually tapering. They 

 are composed of rather short, sharply cuneate pieces, which at 

 the upper margins form a thickened rim, which projects beyond 

 the lower end of the succeeding joint. The rim increases grad- 

 ually in prominence in the upper parts of the arms, especially 

 at the pinnule-bearing side of the plates where it bulges out 

 considerably, giving to the arms their characteristic zigzag ap- 

 pearance. The proximal arm plates, next to the brachials, are 

 longer than the succeeding ones, at their lower face as wide as 

 these, and somewhat constricted along their middle portions; 

 the others are at their longest side about equal to their width. 

 Pinnules long, and close to the arms very strong. They con- 

 sist of about ten joints, of which the proximal ones are short, 

 the others from twice to three times their width. 



The form and size of the ventral tube is not known, near its 

 base it is composed of longitudinal rows of very regularly 

 arranged hexagonal pieces. 



Column small, indistinctly pentangular ; nodal joints consider- 

 ably higher, especially the lower ones, and projecting laterally. 

 Each nodal joint, from the calyx down, gives off radially sev- 

 eral cirrhi, which are long, slender and directed upward. Near 

 the calyx where the nodal joints come very close together, the 

 cirrhi are so tightly packed that they frequently hide the 

 column, and extend beyond the calyx to the arms. Farther 

 down the column they are wider apart, and reach a length of 

 an inch and a half or more, while their length above is not 

 more than an inch. They are composed of numerous short 

 joints, and end in a sharp point. 



Geological position, etc.: The same as the last. 



Our own collection. 



