36 Cincinnati Society of Natural History. 



limestone; and the name Kaskaskia limestone, or Kaskaskia Group, as 

 I prefer to call it, retained for the upper division of the sub-carbon- 

 iferous formation. 



PoTERiocRiNDS AVETHERBYi, u. sp. (Plate VIII., fig. 1, natural size; 



la, anterior view showing azygos interradials; 16, magnified 



view of part of the proboscis.) 



Column. — The column is composed of alternatel}' thin and thicker 

 joints, and is evidently ver}' long. It is pentagonal at the head, but 

 graduallj^ assumes the cylindrical form below, so that at the distance 

 of three inches below the body the pentagonal form can not be observed- 

 It slightly enlarges as it approaches the junction with the head, prob- 

 abl}^ not in excess, however, of the angles necessary to create the pen- 

 tagonal column. The articulating faces of the plates are strongly 

 marked by radiating furrows, which ornament, hy their serrated edges, 

 the surface of all weathered columns. 



Body. — The length of the bod}' is greater than the diameter. It is 

 nearly obconoidal, or rather, regularly expanding from the column to 

 the second radials. The plates are smooth and slightly convex. The 

 sutures are well defined. 



Basal pieces. — There are five pentagonal basal plates, each of which is 

 a little longer than wide. The two longer sides of each join the adja- 

 cent basal plates; the two shorter ones form the upper sloping sides, 

 upon which the subradials rest; and the other side articulates with one 

 of the five sides of the pentagonal column. 



Subradials. — Three of the subradials are hexagonal, and two hepta- 

 gonal. The two longest sides of each plate join with the adjacent sub- 

 radials; the two shortest sides meet the basals below; and the super- 

 ior sides of the hexagonal plates support the first radials above. The 

 heptagonal plate on the left of the azygos interradius, supports upon 

 its upper truncated side the left anterior first radial, upon its left super- 

 ior sloping side the second left anterior first radial, and upon its right 

 superior sloping side the first az} gos iuterradial. The other heptagonal 

 plate is situated more directlv beneath the azygos interradius. It 

 supports upon its upper slight!}' truncated side the second azygos iu- 

 terradial; upon its left superior sloping side the first azj^gos interra- 

 dial; and upon its right superior sloping side the right anterior first 

 ladial. 



First radials. — The first radials are pentagonal and wider tlian long. 

 The upper strongl}' truncated side of each upon which the second ra- 



