272 PALEONTOLOGY OF ILLINOIS. 



and F.Juvenis, Hall, Jour. Bost. Soc, N. H., vii, 317 and 319), possess pre- 

 cisely the same structure, being both described as having small basal and sub- 

 radial pieces. Nor can we make the presence of interaxillary pieces (which 

 occur in both groups), or the small patelliform supplementary pieces, so often 

 seen at the sutures of the radials and arm-joints in well defined Forbesiocri- 

 nus, a means of distinction, since they are not always present in otherwise 

 typical foi-ms of that group, with the interradial spaces filled with plates; 

 while well marked species of Taxocrinus, such as T. Thiemei and T. juvcnis, 

 Hall (sp.), the first without anal or interradial pieces, and the latter with 

 the "interradial and anal series, consisting of one plate each," are described, 

 the first as having " arm joints showing the small patelloid plates very dis- 

 tinctly," and the latter, with ' : the small patelloid plates indicated by the strong 

 curvature of the suture lines of the radial plates, becoming more distinct in the 

 arm plates." So if we attempt to distinguish these groups at all, we must fall 

 back upon the difference of the one group being without anals or interradials, 

 or with but one, two, or three ranges of these pieces, and the other with a 

 greater number. 



The typical forms of this genus range from the Upper Silurian to the top of 

 the Subcarboniferous; while those belonging to the Forbesiocrinus group, are 

 mainly confined to the Subcarboniferous, only a few species apparently of this 

 type having been described from the Devonian rocks. 



Taxocrinus semiovatus, M. and W. 



PI. 20, Fig. 4 a, 4b. 



Forbesiocrinus ? semiovatus Meek and Worthen, Sept., 1860. Proceed. Acad. Nat. Sci., 



Philad., p. 389. 

 Taxocrinus semiovatus, Meek and Worthen, Aug., 1865. Proceedings Acad. Nat. Sci., 



Philad., p. 450. 



Body? below the first bifurcation of the rays, narrow semio- 

 vate, a little wider than long, expanding rather rapidly from 

 the column to the summit of the first radial pieces, above which 

 it widens more gradually, or becomes nearly cylindrical ; com- 

 posed of moderately thick, smooth or subgranulose plates, uni- 

 ted by linear sutures. Basal plates hidden by the column, or 

 merely forming a narrow ring at the connection of the column 

 with the body. Subradials of moderate size, wider than long, 

 three of them on the anterior side pentagonal, the upper sloping 



