514 PALAEONTOLOGY OF ILLINOIS. 



■summit there are six other mammillary plates of smaller size forming 

 three-quarters of a circle, the opening being on the anal side, and 

 bsside these there are from one to three other protuberant plates on the 

 summit of each ray making in all from eighteen to twenty protuberant 

 plates on the vault. First interrradial a little larger than the second 

 radials, hexagonal, and supporting two smaller pieces above, that extend 

 up nearly to the base of the arms. Anal opening minute, slightly pro- 

 tuberant, and located immediately at the base of the mammillary plate 

 that forms the apex of the summit. Surface of all the plates finely 

 rugose. 



Dedicated to Dr. Geo. TV. Kellogg, of Keokuk, Iowa, from whom I 

 received the typical specimen. 



Position and locality : Keokuk, Iowa ; Keokuk limestone, Lower Car- 

 boniferous. 



Genus SYKBATHOCBIKTTS Phillips. 



Synbathocrinus robtjstus, Shumard. 



PI. 29, Kg. 4. 

 Synbathocrinus robitstus, Shumard, 1866. Trans. St. Louis Acad, of Science, Vol. 2, p. 397. 



" Body below the second radials depressed conical, enlarging rapidly 

 from the base, width not quite double the bight, plates thick, surface 

 finely granulose. Base pentagonal above, short, widely truncated and 

 excavated below by the upper joint of the column, margin of excava- 

 tion finely but distinctly crenulate. First radials wider than high, quad- 

 rangular, gently convex, double the "bight of the base ; facets for second 

 radials broad." The foregoing is Dr. Shumard's original description, 

 to which the example figured enables me to add the following : Second 

 radials quadrangular, wider than high and tapering very gently upward 

 Arms stout and composed of slightly rounded plates from one-half to 

 one-third as high as wide, forming when closed a cylindrical prolonga- 

 tion which in the example figured is about 2.60 inches in length. Column 

 round, and composed of rather short plates, of which about every fourth 

 one is a little longer and wider than the others, forming rim-like projec- 

 tions. 



Position and locality : Greene county, Illinois, and Buttonmould Knob, 

 Ky. ; Keokuk Group, Lower Carboniferous. 



