42 



ondary radials are smaller than the first and the arms in each 

 radial series are drawn close together, leaving wide interradial 

 spaces. There are only ten ambulacral openings, in this 

 species, and they are directed upward so as to be hardly visi- 

 ble in a side view. The second secondary radials are broken 

 away from some of the rays in the specimen illustrated. 



The first regular interradials are the largest plates in the 

 body, except the first azygous plate, longer than wide, and 

 have nine sides. They are most tumid at the upper third. 

 The second regular interradials are about one-third as large as 

 the first, heptagonal, and the two superior sides unite with 

 two elongated plates belonging to the vault and the two short 

 superior lateral sides unite with small plates that form part of 

 the covering for the ambulacral channels. The azygous area 

 is larger than the regular interradial areas and the first plate 

 is the largest in the body. It is followed by three plates in 

 the second range, the two lateral ones being small and quad- 

 rangular, while the middle one is large and heptagonal. The 

 lateral plates each abut upon a small plate that forms part of 

 the covering of an ambulacral channel, and the middle one 

 abuts upon two of these plates and upon two elongated plates 

 that belong to the vault. 



The vault is very slightly convex and is depressed in the 

 interradial areas and bears a short subcentral proboscis. It is 

 covered by two circles of plates and two or three small inter- 

 calated ones. The plates appear to have been granular. 

 There are ten ovarian apertures; one on each side of each pair 

 of arms and near the ambulacral openings. 



This species most resembles D. bulbaceus, but differs in form 

 by being less globular, wider in proportion to its height, in 

 having a shallower concavity below and less elevated vault. 

 But the most distinctive difference is in the azygous areas. In 

 D. bulbaceus the azygous area is like the regular areas and 

 has only one plate, in the second range, while in this species 

 the areas are very different, and there are three plates in the 

 second range. In this species there are ten ovarian pores, and 

 in that species none have been discovered. There is also some 

 difference in the surface ornamentation, so that the two species 

 cannot be mistaken for each other. 



Pound in the Hamilton Group, at Charlestown, Indiana, and 

 now in the collection of Mr. J. F. Hammell, of Madison, Indi- 

 ana. 



