CLASS III CRINOIDEA 211 



latter condition is the longest lived, persisting to late in the Carboniferous, while the former 

 did not survive the Devonian, and was chiefly confined among the Fistulata to Ordovician forms. 

 The superradial, or ariu-bearing portion of the plate, is in sonie earlier forms nmch the 

 sinallest part, resting on the right Shoulder of the inferradial, or lower portion ; in others it 

 is nearer equal to, and directly in line with the inferradial ; in later forms it is pushed to the 

 right by the gradual increase in width of the posterior interradius or ventral sac. 



The inferradial, because of its supporting the sac, as is usually the case among the later 

 forms, has received the name of radianal. Primitively, however, as was shown first by 

 Wachsmuth and Springer, and subsequently by Carpenter and Bather, the radianal represents 

 the lower portion of the right posterior radial ; and it has, therefore, nothing in common 

 with the anal plate, which is a specialised interradial. The phases exhibited by the radianal 

 in its progressive structural development furnish excellent differential characters. From its 

 ])riniitive radial position directly und er the right posterior ray, it shifts upward to a left 

 oblique position, and is then eliminated in the later Carboniferous, substantially parallel to its 

 course in the Flexibilia. 



Under the Fistulata are included the foUowing families ; Hyhocrinidac, Meter ocrinidae, 

 A7iomaloerinidae, Calceocrinidae, Catillocrinidae, Belemnocrinidae, comprising the monocyclic 

 forms ; and Dendrocrinidae, Crotalocrinidae, Cyathocrinidae, with subfamilies Carahocrininae, 

 Gaster ocominae and Gyathocrininae ; Botry ocrinidae ; Poieriocrinidae, with subfamilies 

 Poteriocrininae, Graphiocrininae and Encrininae, comprising the dicyclic forms. 



Family 1. Hybocrinidae Zittel. 



Monocyclic ; basals five. Eadials large ; the right posterior radial Compound ; 

 the inferradial almost as large as the other radials, supporting on its right Shoulder 

 the superradial, and on its left the first plate of the tube, or anal plate, which does not 

 enter the dorsal cup. Ventral tube or sac in its most- primitive form, extending hut 

 little above the rest of the tegmen ; superradial very small, sometimes undeveloped. 

 Arm facet small, round, less than width of radial; arms simple, uniserial, mm- 

 pinnulate. Orals large, with ambulacra resting on their adjacent edges ; posterior 

 one pierced by hydropore. Lower Ordovician. 



Hybocystis Wetherby. Three of the rays bearing primitive arms composed 

 of but few joints, with ambulacral furrows passing from the ventral to the dorsal 

 side of the arms, and continued upon the surface of the R. The two other 

 rays are without arms, and the ambulacra follow the surface of the calyx, and 

 may pass down so far as to enter the basals. Anus through a 

 valvulär pyramid surrounded by integument of small plates 

 between posterior oral and distal edge of the anal plate. Stem 

 round. Ordovician (Trenton) ; Kentucky and Canada. 



Hybocrinus Billings. Similar to Hybocystis, but with five 

 regulär arms, and no recurrent ambulacra. Anus either 

 through a valvulär pyramid or simple opening. Ordovician 

 (Trenton) ; Canada and Kentucky. ^^°' ^^^' 



Hoplocrinus Grewingk (Fig. 312). Like the preceding, ^Z'^^G^ZinÜ: 

 but with the inferradial sloping only to the right, and sup- ordo^^ijian^^ ^^st. 

 porting a small, trigonal superradial. On the left it supports seen irrom the anai 

 small plates of the ventral sac, without the Intervention of a ^if^k).^*^^' °'" 

 larger plate. Ordovician ; St. Petersburg. 



Baerocrinus Volborth. Like Hoplocrinus, but the right posterior and the 

 anterior ray without arms; apparently inferradials only are developed. 

 Ordovician ; St. Petersburg. 



Family 2. Heterocrinidae Zittel. 



Monocyclic ; basals five. Galyx usually elongate conical. One or mwe of the 

 radials Compound. The superradial of the right posterior ray supporting to the 



