12 



miliary radials arc smaller than the first and the arms in cadi 

 radial series arc drawn close together, Leaving wide Lnterradia] 

 spaces. There are only ten ambulacra! 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 oi the rays in the specimen illustrated. 



The first regular interradials arc 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 ambulacra! channels. The azygous area 

 is Larger than the regular Lnterradia! areas and the tirst plate 

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

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

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

 lateral plales each abul upon a small plate that forms part of 

 tin 1 covering of an ambulacra! 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 

 Lnterradia! areas and hears 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 ol each pair 

 of arms and near the ambulacra! openings. 



This species most resembles IK bulbaceus, hut differs in form 

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

 having a shallower concavity below and less elevated vault. 

 Bu1 the mosi distinctive difference is in the azygous areas. In 

 I), 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 

 cannol he mistaken for each other. 



Pound hi the Hamilton Group, ai Charlestown, Indiana, and 

 now in the collection of Mr. .I. l-\ Hanimell. of Madison. Indi 

 ana. 



