120 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



GENUS POTERIOCRINUS ( Miller). 



POTERIOCRINUS NASSA ( n. s.). 



Body turbinate : base comparatively broad, pentangular, witli the 

 column-scar strongly marked, and its angles corresponding to the 

 sutures of the plates. Basal plates pentagonal, longer than wide, 

 the lateral angles at the base a little prominent, corresponding to 

 the form of the column : subradial plates hexagonal (except on 

 the anal side) and subequal, nearly once and a half as long as 

 wide; radial plates shorter than their width, hexagonal (except on 

 the anal side), broadly truncate above, with the margin thickened 

 for the attachment of the strong arm-plates. The subradial plates 

 are prominent and subangular along the middle, and somewhat 

 abruptly depressed at the sides. 



Surface smooth or finely granulose. 



Geological formation and locality. In the shales of the Hamilton group, 

 near Canandaigua, N.Y. Collected by R. P. WmxFiELD, 1858. 



POTERIOCRINUS NYCTEUS (n.s.). 



Body turbinate : height and greatest width nearly equal. Basal 

 plates a little longer than wide : subradial plates about one-fourth 

 longer than wide : radial plates nearly twice as wide as long, 

 prominent above, the upper margin thickened and projecting; a 

 little depressed between the centre and the lateral margins, the 

 latter slightly thickened at the suture line. 



Arms bifurcating on the third joint from the base, composed of 



^ rounded joints which are once and a half as long as wide, con- 

 tracted in the middle and swelling at the extremities : every 

 second joint on the opposite sides give origin to armlets of similar 

 character to the arms. The tentacula undetermined. Proboscis 

 nearly three times as long as the body plates. 



Plates on the anal side comparatively large, supporting on the 

 upper margins the plates of one side of the strong elongate pro- 

 boscis, hexagonal, wider than high, and gradually diminishing in 

 size from the base. Upper anal plate, and plates of the proboscis, 

 marked by radiating subangular ridges towards the margin. Plates 

 of the body and arms striato-granulose, the striae arranged in a 

 radiating direction. 



Column round, comparatively strong; the upper part composed of 

 joints of unequal length, in a somewhat regularly alternating 



