CONTRIBUTIONS TO PALAEONTOLOGY. 121 



order; and below this, of nearly equal joints which are about 

 half as long as wide, with strongly crenulate margins. 



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

 Ontario county, N.Y. C. A. White, collector. 



POTERIOCRINUS DIFFUSUS ( n. s.). 



Body small, turbinate. Basal plates small, about as long as wide : 

 subradial plates less than one- fourth longer than wide, prominent 

 in the middle : radial plates short, much wider than high, the 

 upper margins thickened and projecting. Three plates are visible 

 in the anal area, the lower one of which is subpentagonal, the 

 two lower sides resting on adjacent subradial plates. The three 

 lower arm-plates are wider than long. 



Arms bifurcating on the third plate, giving ten arms, which are long 

 and slender, widely diverging, composed of long cylindrical joints 

 curving alternately on opposite sides, and giving a zigzag direc- 

 tion to the arms. Every second or third joint gives off armlets, 

 which are composed of joints similar to those of the arms, but 

 proportionally longer : intermediate joints shorter than those 

 bearing the armlets. No tentacula proper have yet been observed. 



Surface of the body granulose. Column round; the upper part 

 consisting of thicker and thinner joints, with the edges rounded. 



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

 Ontario county, N.Y. C. A. White, collector. 



POTERIOCRINUS NEREUS ( n. s.). 



Body small, subpentagonally turbinate. Basal plates short, minute, 

 forming a narrow rim about the base of the body : subradial 

 plates longer than wide : radial plates shorter than the subradials, 

 thickened at the upper margins. First arm-joint short; second one 

 much longer, and thickened at the extremities. Arms bifurcating 

 on the second joint from the radial plate; the joints nearly twice 

 as long as wide, rounded and thickened at the extremities, and 

 giving origin to slender jointed tentacula. Surface granulose or 

 granulose-striate, sometimes apparently smooth. 



Column obtusely subpentangular near the base of the body, and 

 composed of joints of unequal thickness. 



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

 Ontario county, N.Y. Collector C. A. White. 



[Senate, No. 116.] 16 



