106 (Jincinnati Society of Natural History. 



situated in a line drawn across the exterior part of the adjoining arm 

 bases. 



The third range of plates, descending from the ambiilacral orifice, 

 consists of eight plates and embraces the mouth. Six of these are 

 heptagonal, the seventh side being produced by the intercalation of 

 small plates, between alternate plates, on the ambulacral side of this 

 range and the next full range of plates below. The plate upon the 

 left of the mouth, including the mouth-side, is pentagonal, and the 

 plate upon the right of the mouth, including the mouth-side, is hexag- 

 onal. I have not included in this range the plate upon the lower side 

 of the mouth. The mouth is thus placed close to the anterior side, 

 and in the third range of plates in descending order. Part of the 

 plates surrounding the mouth are removed in our specimen, but the 

 scar shows the elliptical outline of the mouth. 



The fourth range may be called an imperfect range, because it is 

 separated on the ambulacral side, and includes only the alternate in- 

 tercalated plates. The rapid expansion, however, of the bod}^ upon 

 the right and posterior sides, and the smaller size of the plates gives 

 us twelve plates in this range: ten of them are joined together, and 

 two of them are the separated intercalated plates upon the ambulacral 

 side. One of the plates abuts upon the lower side of the mouth. 



The fifth range is injured in our specimen, so that it is a matter of 

 some doubt, whether it consists of eight or nine plates, but the inde- 

 terminable space is only the width of one of the other plates, and, 

 therefore, we conclude, it consists of eight plates. This range is well 

 nigh broken in the posterior part of the ambulacral side, where two 

 plates unite only at an angle instead of b^^ their sides. 



The sixth range is composed of about twice as many plates, as ten 

 plates shown, in our specimen, abut upon five in the fifth range. Only 

 part of the seventh, eighth, ninth and tenth ranges are preserved, in 

 the specimen illustrated; enough, however, to show that the plates are 

 of unequal size and not regularly disposed into ranges. Another 

 specimen shows, that, at about the tenth or eleventh range, the body 

 begins to taper for the column below, but we are not able to describe 

 the plates upon this part of the body. 



The surface of the i)lates is pustulated, and numerous pores pene- 

 trate the bod}^ through these pustule-like prominences, but between 

 them the plates appear to be barren of pores. 



This species was collected by Fred. Braun, Esq., and the author, 

 near the base of the Niagara Group, in Ripley county, Indiana; the 

 specimens described, however, are in my collection. 



