46 



three elevated subspinous plates in the center, and otherwise 

 covered with polygonal, convex and spinous plates. A spinous 

 plate is over the line that separates the double arm opening in 

 each of the five radial series. The azygous opening is near the 

 margin. 



This species is the same mentioned in Volume V, page 537, 

 of the Geological Survey of Illinois, under the name of "Dichocri- 

 nus cornigerus, Schumard?" and the calyx of which is figured, 

 under that name on plate 20, Fig. 6a, 6b, and 6c. The calyces 

 of the two species, though somewhat different, resemble each 

 other, but the resemblance disappears when the calyx and vault 

 are found together. In T. cornigerus, the vault is much larger 

 than the calyx and constructed on a different plan from the 

 vault in this species so that the vaults could not be mistaken 

 for each other, in any case. In this species the calyx is larger 

 than the vault, and the depressed interradial spaces and pro- 

 longed radial areas are peculiar. The azygous areas have little 

 resemblance in the two species. 



Found in the St. Louis Group, at Eose Claire, in Hardin 

 county, Illinois, and now in the collection of Wm. F. E. Gurley. 



