66 



the third range, and, as they are different from those in other 

 species, we will call particular attention to them, by com- 

 mencing at the one at the azygous orifice and following the 

 range to the right. One abuts the middle upon the azygous 

 orifice and each lateral side on a summit plate at the superior end, 

 which make the plate heptagonal. The next one abuts two summit 

 plates and is hexagonal. The next four summit plates and is hep- 

 tagonal because there are only three sides below the summit. 

 The next one also abuts four summit plates and is heptagonal, 

 but one of the four summit plates belongs to the circle that 

 surrounds the central summit plate. The next one is hexa- 

 gonal, very wide below and narrow above and abuts two 

 summit plates. The next one is hexagonal and abuts two 

 summit plates. The next one has ten sides and abuts the 

 superior end against seven summit plates one of which belongs 

 to the circle that surrounds the central summit plate. The 

 next one has ten sides and abuts six summit plates or those 

 surrounding the ambulacral orifices, and the next one abuts 

 three plates belonging to the summit and is heptagonal. 



The central summit plate is surrounded by a circle of seven 

 plates, two of which abut upon the plates of the third range, 

 as above described, and between these two plates there is a 

 cluster of arms opposite to the mouth. The mouth is depressed 

 below the level of the summit and is surrounded by six plates, 

 two of which belong to the circle of seven plates and one be- 

 longs to the third range of body plates. The two plates that 

 abut upon the plates belonging to the third range, are also 

 depressed below the level of the summit, and the vault is thus 

 divided into three areas which contain the arm clusters and 

 the smaller summit plates about the orifices. 



There are five arm openings in the cluster opposite to the 

 mouth, four in the cluster on the right of the mouth and eight 

 in the cluster on the left of the mouth. There are, therefore, 

 seventeen ambulacral openings in this species. 



This species is distinguished by its general form, by having 

 nine plates instead of eight or less in the third range and by 

 the form of the summit and number of arms. 



Found in the Niagara Group, in Madison county, Indiana, by 

 J. F. Hammell, in whose honor we have proposed the specific 

 name and now in his collection. 



