58 [Assembly 



three plates ; the first one large, wider than high, and a little 

 projecting at the upper margin ; second one short and wide, 

 quadrangular, a little constricted in the middle. The third 

 radials are obtusely wedgeform above and strongly constricted 

 in the middle, and supporting a single arm on each upper sloping 

 face. 



Arms simple throughout, composed of elongate subcylindrical 

 joints which give origin to strong jointed tentacula from near 

 the upper margin of their longer sides. These arm-plates are 

 enlarged at the origin of the tentacula which are given off 

 alternately on the two sides of the arm, giving it a tortuous 

 direction. Plates of anal area large in the lower part, and gra- 

 dually decreasing above. 



Column proportionally strong, subpentagonal, composed of alter- 

 nating longer and shorter joints; the longer ones are wider, 

 and subnodose on the periphery. 



Surface of plates granulose ; those of the body slightly convex. 



This species is closely related to Poteriocrinus diffusus of the Hamilton group; 

 but differs in having a shorter and comparatively broader body, the basal plates in 

 that one being much longer than in this. In the arms of this one, every joint bears 

 tentacula; while in the Hamilton species, it is only every second or third joint which 

 bears tentacula. In their general appearance, the two species offer few points of dis- 

 tinction. 



The Poteriocrinus diffusus of the Hamilton group occurs at some distance below 

 the Genesee slate, in beds originally designated Moscow shales. Above this horizon 

 we have the Genesee slate and Portage group, which may be stated at one thousand 

 feet; and to this thickness must be added nearly one thousand feet of beds belonging 

 to the Chemung group of New- York, before reaching the horizon to which these 

 fossiliferous beds in Ohio have been referred by some geologists. 



SCAPHIOCRINUS (POTEEIOCRINUS) LYRIOPE (n.s.). 



Body small, subturbinate. 



Arms slender and simple, originating on the second radial plate, 



which is much longer than wide, and moderately constricted in 



the middle. 



In its general features, this species resembles Pater, mgina, being only a little 

 more delicate in its parts. The form of the calyx is similar, though scarcely so much 

 spreading. The second radial plate is a bifurcating plate (instead of the third), and 

 is much longer than the third plate in the other species. The arms and tentacula are 

 more slender; the arm-plates not so prominent at the junction of the tentacles, and 

 therefore not so tortuous in their direction. The surface of both the body and arms 

 are more distinctly striato -granulose. The column is apparently round, and the 

 plates not so unequal as in the other species. 



There are several individuals of each of these species, and the characters are 

 constant, leaving no doubt of their distinction. 



SCAPHIOCRINUS SUBCARINATUS (n.s.). 



Body small, subturbinate, with elongate slender branching arms. 

 Basal plates very minute, triangular or subpentagonal : sub- 

 radials small ; first radial plates wider than high ; second ra- 

 dials longer than wide and strongly constricted in the middle, 



