172 CRINOIDS. 



as the radials, quadrangular, as wide again as long, and raised 

 in the center. Second costals pentagonal, twice as wide as 

 high. Priirary interradials rather large, as wide as long; sec- 

 ondary interradial pieces small, elongated, and somewhat irreg- 

 ular. Principal anal ossicle like the radials, but a little longer 

 and narrower, bearing upon its upper edges three smaller 

 pieces, and these again supporting several plates. The ven- 

 tral parts have the following arrangement: Over every pair 

 of distichals is a rather large pentagonal piece, whose inferior 

 angle corresponds to the axis of the costals, and on each side 

 of this plate is an elongated ossicle of irregular form, which 

 lies over the interradials ; these three pieces form the inferior 

 segment of a circlet of seven plates, in the center of which is 

 a large spinous or nodose plate. oS'ear the center of the disk 

 is a large tumid piece encircled by four orals and several other 

 smaller plates. Surface marked only by a single large node in 

 the center of each plate of the dorsal cup ; other ossicles 

 slightly convex, smooth. 



Horizon and localities — Lower Carboniferous ; Upper 

 Barlington limestone: Ash Grove, Palmyra, Sedalia, Hanni- 

 bal and Louisiana. 



The above description is somewhat abbreviated and modi- 

 fied from the one given originally by Dr. Shumard. The form 

 is one of the most characteristic crinoids of the upper Burling- 

 ton limestone, and is widely distributed in space. The ven" 

 tral spines, as in all the spiniferous species of the genus, are 

 seldom preserved, so that merely a large, circular tubercle is 

 ordinarily observed. 



Dorycrinus cornigerus (Hall). 



Aciinocrinus cornigerus Hall, 1858: Geol. Iowa, vol, I, p. 576, pi. ix, 



fige. 12a-c. 

 Aciinocrinus corni^erws Hall, 1860: Geol. Iowa, vol. I, Supp. pi. iii, 



fig. 4. 

 Aciinocrinus divaricatus Hall, 1860: Geol. Iowa, vol. I, Supp. p. 11. 

 Aciinocrinus quinquelohus Hall, 1860: Geol. Iowa, vol. I, Supp. p. 15. 

 Dorycrinus cornigerus Meek & Wortben, 1873 : Geol. Sur. Illinois, vol. V, 



p. 380. 

 Dorycrinus quinquelohus Meek & Worthen, 1873: Geol. Sur. Illinois, vol. 



V, p. 380. 



