116 Cincinnati Society of Natural History. 



seems to prevail over the dome. The base of a proboscis is shown, 

 in the anterior third of the dome. The dome is also possessed of five 

 spinons plates. One of these is on the posterior part, behind the pro- 

 boscis; one on each side of the proboscis, a little more than half way 

 to the arm bases; and one behind each of the latter, near the arm 

 bases, and a little anterior to the posterior spine, first above mentioned. 



The column is round, of medium size, composed of alternately thick- 

 er and thinner plates, the thicker projecting beyond the thinner ones, 

 and the articulating f«,ces furrowed by radiating lines. The pentagonal 

 opening is rather large. 



This species was collected by Prof. W. H. Colvin and the author, in 

 the Upper Helderberg or Corniferous limestone, at the stone quarries 

 near Columbus, Ohio. The specimens illustrated are in my collection. 

 The specific name is from the cap-like form of the body. 



Stephanockinus osgoodensis, n. sp. 



Plate X., fig. 7, natural size. 



fig. la, magnified two diameters. 



Body small, obconoidal, triangular at the base, or rather hexagonal, 

 because three very obtuse angles are formed, at the junction of the 

 plates, and slightly pentagonal above. 



The basal plates are longer than wide, and united, leave a small de- 

 pression, at the base, for the columnar attachment. Each plate is 

 sharply angular, in the middle of the lower half, but the angle fades 

 awa}^ in the upper half. An obtuse angle is formed, at the junction of 

 the plates, in the lower halt, which also fades away, in the upper half. 

 The three basal plates, therefore, form an hexagonal outline, in the 

 lower half, marked by three sharp angles in the middle of the plates, 

 and three obtuse angles, at the sutures. These angles fade away in 

 the upper half, and are not continued on the radials. Two of the basal 

 plates are hexagonal, having each three upper sides, and are of equal 

 size. The other plate is smaller, in the upper half, and having only 

 two upper sides, is pentagonal. 



The five radial plates form obtuse angles, at the sutures, but the 

 plates are a little convex, which well nigh destroys the pentagonal ap- 

 pearance of the body. These plates are a little longer than wide, three 

 of them are heptagonal and two hexagonal. The heptagonal plates 

 have two lower sides, eacli of which is supported, upon a basal plate, 

 while the hexagonal plates have only one lower side resting upon a 

 basal plate. The upper margin of each plate is deeply excavated, for 

 the reception of the psendo-ambulacral structure. 



The plates of the third range are very small, if they exist at all. The 



