114 Cincinnati Society of Natural History. 



upper sloping sides two of the smaller radials; it, is, therefore, an he^- / 

 agonal plate, much wider than long. 



Two of the smaller radial plates unite over the middle part of the 

 hexagonal plate, upon which, they rest their longer arcuate sides. 

 The other inferior side of each is much shorter, and rests in a little 

 arcuate notch, in the superior part of the adjoining larger radial. The 

 other smaller radial plate is supported between the two larger radials, 

 by a small arcuate side, in the superior part of each. 



The species as may be seen from the foregoing description has five 

 arms, three of which are supported upon the smaller radials, and the 

 other two b}^ the larger radials. Our specimens do not preserve the 

 arms, but the arm bases are comparatively' large, for such small speci- 

 mens, and show that the arms must have been crowded close together. 

 One of the arm plates possesses a ver}^ wide and deep ambulacral fur- 

 row, for so small a plate. The column is small and round. 



This is the first species described, in America, that has been re- 

 ferred to the genus, Pisocrinus, of M. de Koninck. It is distinguished 

 from the European species by the shape of the plates. In the European 

 species, two of the basal plates unite in an angle of the triangular 

 figure formed by the basal plates, and, therefore, only one side of the 

 triangle is formed by the sides of three basal plates. The other two 

 sides, being each formed, by two sides of the basal plates. In our 

 species, two of the sides of the triangle, formed by the basal plates, 

 are each made by the sides of three basal plates, and only one by the 

 sides of two basal plates. In the European species, the large plate, occu- 

 LJ^^ pying the position of the he/agonal plate, in our species, is pentagonal. 

 It rests upon two basal plates, while, in our species, it rests upon three. 

 The arm bases are also quite distinct, in their shape; but as our species 

 falls into the generic formula of Pisocrinus, we regard these distinc- 

 tions as of only specific importance. Moreover the j^enus Pisocrinus 

 is only known, in Europe, in rocks of upper tsilurian age. 



This species was collected by the ardent and indefatigable palaeonto- 

 logist, Fred. Braun, Esq., and by the author, in the lower part of the 

 Niagara Group, in Ripley county, Indiana; the specimens illustrated, 

 however, are from n\y collection. 



Megistocrinus pileatus, n. sp. 

 Plate X., fig. 1, (liagrainmatieal view from a flattened specimen, 

 fig. la, summit view, 

 fig. lb, basal view. 



The body is deeply depressed, for the columnar attachment; sub- 

 circular at the arms, being slightly elongated from the anterior to the 

 posterior side; and convex on the dome. 



