INTEETEBRATES. 403 



heptagonal. First radial pieces nearly one-third wider than high, being 

 as wide as the subradials, bat shorter, and not so tntnid ; all pentago- 

 nal, with the upper side truncated their entire bre.idth. Succeeding 

 radials, of which there are three in each of the rays seen,* as wide as 

 the first, but much shorter, or ouly one-third to one-fourth as long as 

 wide, thus forming free arms so wide as to be nearly in contact all 

 around except on the anal side ; last or fourth radial supporting upon 

 its superior slightly slopiug sides the first divisions of the arms, which, 

 at least in one of the posterior, and one of the lateral rays, bifurcate on 

 the third piece, while some of the divisious appear to divide again on 

 the fourth piece, which is as far as they can be traced in the specimens 

 examined. Column large, or nearly two-thirds as wide as the base at 

 its connection with the latter; but suddenly tapering downwards, and, 

 at least in one of the examples, ending with the sixth piece in a rounded 

 point, evidently showing this individual to have been free at maturity. 



Connecting or upper joint of the column in the only two examples 

 seen, very thick, and in one quite tumid. 



Hight to summit of first radial pieces, 0.48 inch ; breadth at top of first 

 radial pieces, 0.50 inch ; hight of base, 0.20 inch ; breadth of rays below 

 the. first division, 0.17 inch. 



This species seems to be most nearly related to H. polydactylus of 

 Shumard, from which it differs in the remarkable narrowness of its 

 base, and the proportional greater thickness of its column. It also 

 differs in having only three to four primary radials to each ray, instead 

 of five or six. 



Locality and position: Mount Carroll, Illinois, in the Cincinnati 

 Group of the Lower Silurian. 



Heteeoceinus ceassus, M. and W. 



PI. 23, Fig. 1. 



Meterocrinu'fi cras8us t Meek and Worthen, 1865. Proceed. Acad. Nat. Sci., Philad., p. 147. Geol. 

 Survey of 111., Vol. III., p. 334. PI. 4, fig. la, b, c. 



For the use of the very fine specimen figured in this volume, I am 

 indebted to Mr. Stewabt, of Piano, Kendall county, Illinois. 



* The right posterior ray seems to be an exception to this statement, as it appears to have only three 

 radials including the first, with the secondone nearly as large as the first. Its parts, however, are not 

 well preserved. 



