152, ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
radial. On the left it supports small plates of the ventral sac, without the 
intervention of a larger plate. Ordovician; St. Petersburg. 
Hybocystes, Wetherby. Arrangement of calycine plates the 
same as in /Hybocrinus, but differing in the arm structure. 
Three of the rays bearing primitive arms composed of but 
few joints ; ambulacral furrows passing from the ventral to 
the dorsal side of the arms, and continued upon the surface 
re: of the f. The two other rays are without arms, and the 
Hoplocrinus di- ambulacra follow the surface of the calyx, passing down so 
et: as "&e far as to enter the basals. Ordovician ; Kentucky. 
PSUs ee. Baerocrinus, Volborth. Like Hoplocrinus, but the right 
side (after Gre- posterior and the anterior ray without arms; apparently 
wingk). 5 A d ae ; 
inferradials only are developed. Ordovician ; St. Petersburg. 

Family 2. Anomalocrinidae. Wachsmuth and Springer. 
Base monocyclic. Radials very irregular in form, the right posterior and left 
antero-lateral ones compound, all of them laterally in contact. Ventral sae small, 
tubular ; its lowermost plate vesting in the angle formed by the superradial to the right, 
and the upper end of the simple radial to the left. Arms uniserial, bifurcating at 
intervals. Pinnules or small armlets given off from each arm-joint on one side only, 
as far as from one bifurcation to the next, when they change to the opposite side. 
Ordovician. 
Anomalocrinus, M. and W.  B five. Unique in that the large simple 2 of 
the posterior ray is often longitudinally bisected in the median line. <A small 
quadrangular supplementary piece enclosed within the basal ring. Tegmen 
composed of large plates. Column strong. Ordoyician; North America. 
Family 3. Heterocrinidae. Zittel (emend. W. and Sp.) 
Base monocyclic ; basals five ; one or more of the radials compound. The infer- 
radial of the right posterior vay supporting to the right the superradial, and to the left 
the ventral sac. Anals absent. Arms wniserial. Ordoyician and Silurian. 
Heterocrinus, Hall (Stenoerinus, W. and Sp.) Crown sub-eylindrical, calyx 
small, arms long. Three of the 2 compound ; the others simple, and shorter. 
The inferradial of the posterior ray has the form of an axillary, supporting to 
the left the ventral sac, and to the right the superradial. Arms comparatiy ely 
stout, giving off long branchlets at intervals, which often branch again. 
Column very large, pentagonal, and quinquepartite ; the lines of suture infers 
radial in position. Ordovician ; North America. 
Eetenocrinus, 8. A. Miller (Heterocrinus, W. and Sp. non Hall). Like the 
preceding, but the arms formed of continuous series of syzygies comprising two 
plates each, the epizygals giving off long armlets. Column of moderate size, 
round, and tripartite ; nal cani al large eal pentalobate. Ordovician ; North 
America. 
Ohiocrinus, W. and Sp. Differs from /Zeferocrinus in the details of its arm- 
structure, and in the form of the ventral sac. Arms ten, long, and giving off 
from every third or fourth joint long filiform armlets, which extend to the full 
height of the main arms. Ventral tube resting upon the left sloping side of 
the right posterior inferradial (2.4), and ascending spirally with the adjacent 
