510 PALAEONTOLOGY OF ILLINOIS. 



treinely short. Impressions of the upper side of the slender 

 arms show them to have been somewhat rounded above, with 

 the nearly square arm pieces slightly alternating. Some of 

 the impressions seem to show traces of central pores or pits, 

 one at the middle of each pair of pieces, though in others 

 no traces of these are visible. 



We have numerous specimens of this little species before us, but as 

 they are all merely in the condition of casts and moulds, in a very flue, 

 somewhat granular matrix, they do not show the details of its struct:""^ 

 very clearly. As far as its structure can be made out, however, it seems 

 to agree well with the general features of the genus Pro taster, as illus- 

 trated by Prof. HALL, in the Twentieth Report of the Regents of the 

 University of N. Y. on the State Cabinet of Nat. Hist., though not with 

 Mr. SALTER'S figures of P. Miltoni. It will probably be found to be 

 generically distinct from the Silurian typical forms of Protaxter, but we 

 prefer to place it provisionally in that genus for the present." We are 

 not aware that any well denned species of the genus Protaster, how- 

 ever, have been found in Carboniferous rocks. 



Locality and position Crawfordsville, Indiana. Keokuk division of 

 the Lower Carboniferous series. 



GENUS ONYOHASTEK, M. and W. 

 ONYCHASTER ELEXILIS, M. and W. 



PI. 16, Fig. 3. 

 Geol. Surv. of Hlinoia, Vol. HI, p. 526. Proceed. Acad. Nat. Sci., Phila., 1869, p. 83. 



GENUS PHOLIDOOIDARIS, M. and W. 



Pholidocidaris, MEEK and WORTHEN. Proceed. Acad. Nat. Sci., Phila., 1869, p. 77. 



Entire form unknown. Interambulacral plates rather thin, very 

 irregular in size and form, all strongly imbricating apparently from be- 

 low, and toward the lateral margins of the areas ; arranged in five or 

 more rows, only the outer two of which seem to be continued to the 

 extremities of the areas ; all occupied with generally obscure secondary 

 granules, and most of those on the lower (?) side of the body, also pro- 

 vided with large primary central tubercles and spines ; primary tubercles 

 sometimes showing a small pit in the top, surrounded by two smooth 

 rings, separated by an annular furrow, and all without any ring, de- 



