FOSSILS OF THE CHESTER GROl P. 547 



Dedicated to the memory of the late Gov. WM. H. BISSELL, as a 

 slight tribute of respect for his manifest interest iu the success of the 

 geological survey and the general advancement of science. 



Locality and position Chester division of the Lower Carboniferous, 



-rer. Illinois. 



Si r.-GExrs ZEACRIXUS. 

 Zi: AC KIN is? ARMIGER, M. and W. 



PL 21, Fig. 3. 

 Zeacrinus? armiger, MEEK and WORTHEX. 1?70. Proceed. Acad Xat. Sci.. Phila.. p. 27. 



BODY small and depressed, or nearly basin-shaped, but 

 with the under side rounded, and concave in the middle. 

 Base very small, and nearly or quite hidden in the concavity 

 of the under side. Sub-radial pieces comparatively large, 

 and curving under below, but not tumid or convex; three 

 with a general pentagonal outline, but probably having a 

 sixth obtuse angle at the middle of each below; the other 

 two on the anal side presenting a general hexagonal form, 

 but truncated by the anal pieces in such a manner as to 

 present a heptagons! form, exclusive of the very obtuse 

 angle probably existing at the middle of the under side of 

 each. First radial pieces twice as wide as high, pentagonal 

 in form, and truncated across their entire breadth. Second 

 radials as high as wide, each bearing two arms on their 

 superior sloping sides, and developed into a long, slender, 

 rounded, niucronate spine, which is directed nearly hori- 

 zontally outward. Anal pieces small, and arranged in a 

 double alternating series, the first or lowest piece being 

 somewhat cuneiform and wedged obliquely down between 

 one of the sub-radials and the under side of the first radial 

 on the left, so as to touch, by a very short side, the next 

 Bab-radial on the left; second anal piece resting on the short 

 truncated summit of one of the heptagonal subradials, and 

 connecting on the right with one of the first radial pieces, 

 and on the left with one of the upper sides of the first anal 



