200 PALEONTOLOGY OF ILLINOIS. 



ously arranged; the lower one which is larger generally 

 deeply wedged in between the first radials, so as to almost 

 touch the upper angles of the basals. There are two, three or 

 four plates in the second range, which abut laterally against 

 the adjoining second and third radials, and these are succeeded 

 by 4 or 5 plates of a third row, which are abruptly bent inward 

 at their upper ends almost at right angles, so as to form a 

 sharply defined edge, against which the plates of the ventral 

 covering rest. The latter plates are very minute and irregular 

 in their arrangement, they form a pliable integument, which prob- 

 ably extends over the whole surface and along the rays. The 

 free rays at their ventral side are provided with large pouches 

 which apparently contain the ambulacra. At the azygous side 

 the arrangement of plates is very different; the posterior basal 

 is shorter, truncated instead of angular, and excavated at the 

 upper end for the reception of three or more anal pieces, which 

 are longitudinally arranged and connected with the radials at 

 each side by small plates. 



Column stout; slighely tapering; its upper end composed of 

 very short and even joints, all of equal size and prominence. 



Geological position, etc.: The same as the last. 



This is probably the rarest species at LeGrand, only two spe- 

 cimens having been found; that figured is from the collection 

 of Hon. Delos Arnold, the other in our possession, being 

 kindly presented to one of us by Mr. George Cull, the station 

 agent at LeGrand. 



