19C 



PALAEONTOLOGY OP ILLINOIS. 



Fig. 9. 



From the foregoing form- 

 ula it will be seen that this 

 type agrees exactly with Ac- 

 tinocrinus in the number and 

 arrangement of the pieces 

 composing the body, as far 

 as to the third radial pieces, 

 but differs remarkably in the 

 structure of its rays beyond. 

 These rays, as may be seen 

 by the annexed figure 9, 

 extend out horizontally to 

 a great length, in the form 

 of tubular, free, rigid, arm- 

 like appendages, covered all 

 the way out with small 

 pieces like those of the 



Steganocrinus pentagonus (natural size). . , „ - 



This cut shows the upper side of the body and the cover- Vault; Willie they are COm- 

 ed free rays, with portions of the true arms as given off on -. , n .. 



each side of the rays. Fig. a is an enlargement of one of posed On tlie Under Side 

 the true arms, as seen on the under side. Fig. d shows A 



the structure of the free rays, as seen from above, with r>f fl Sin crip T*fin crp rvf m'opofl 

 the small covering plates removed, so as to expose the Ui ** Bm O le Id-Uge ui pitJCCB 

 internal cavity, with its branches extending out to the / j n n\ s + mTln .l, r 



true arm-bases, alternately arranged on each side. The ^ BCC <*j p* y? oi/IUllgly 



base of the proboscis, and its opening, are seen near the , , . , -, 



centre of the body. curved up on each side, and 



giving off alternately on either side the true ascending arms, 

 composed each of a double series of small alternating pieces, 

 bearing the tentacles. These long, free, arm-like rays, some- 

 times bifurcate on the third radial pieces, while in other in- 

 stances they are simple, being composed of a series of very 

 gf adually diminishing pieces, the first of which scarcely differs 

 from the third radial, upon the truncated upper side of which 

 it rests, or from those following, all of which are in a direct 

 line with the primary radials of the body. Hence in these 

 instances there might be said to be an indefinite number of 

 radial pieces to each ray. 



