INVERTEBRATES. 267 



as wide. The principal arm-pieces are all connected by pecu- 

 liar undulating sutures. Column rather strong, and apparently 

 during the life of the animal, very flexible, rounded near the 

 body, and composed of thin, alternately larger and smaller seg- 

 ments, with sharp edges, which are more or less crenulated; 

 farther down becoming alternately compressed in opposite 

 directions, at intervals of about every five joints, while all the 

 joints increase somewhat in thickness, and are ornamented 

 by short spine-like projections. About every fifth segment 

 more prominent on its edges than the others. Length of body, 

 to the summit of the first radials, about 0.20 inch; breadth, 

 0.26 inch; length of arms, near 1 inch. 



This is an exceeding delicate little species, rather closely allied to a form 

 we have seen in collections, labeled Platycrinus Polydactylies, Troost. It has, 

 however, a smaller body, and the lower joints of its arms are much more dis- 

 tinctly constricted around the middle, and more projecting at the joints on 

 each side. 



Locality and position: Hardin county, 111.; St. Louis division of the Lower 

 Carboniferous series. 



9 



Platycrinus plentjs, M. and W. 



PI. 20, fig. 3. 



Platycrinus vlenus, Meek and Wqrthen, Sept,, 1860. Proceedings Acad. Nat. Sci., 

 Philad., p. 380. 



Body globose, somewhat wider than high, composed of thin, 

 slightly granulose plates, connected by linear sutures, except- 

 ing in the base, where they are anchylosed and carinate. Base 

 depressed basin-shaped, widening rapidly from the rather small 

 columnar facet, which is margined by a small rim. First 

 radials comparatively large, about as high as wide, subquad- 

 rangular in outline, the two superior lateral angles being rather 

 distinctly truncated for the reception of the anal and interra- 

 dial pieces ; all regularly incurved above, where they are each 



