ORDER III CRINOIDEA—FISTULATA 153 
convolutions in contact. Column strong, obtusely pentagonal, and quinque- 
partite. Ordovician ; North America. 
Tocrinus, Hall. B five, small; FP five, the right posterior one compound. 
The lower section of the latter, which serves as radianal, nearly of the same 
size as the other 2, but angular above instead of concave. It supports the 
superradial on the right, and the ventral sac on the left; it is so large as to 
extend considerably above the level of the other /?, thus assuming the aspect 
of an axillary brachial. Ventral sac composed at its posterior side of a longi- 
tudinal row of large, solid, elongate plates ; at the other sides of short, delicate, 
transverse pieces ; the former plates being attached to the £4, are easily mis- 
taken for arm ossicles. Arms without pinnules, branching. Column sharply 
pentagonal ; the angles radially disposed. Ordovician ; North America. 
Herpetocrinus, Salter (Myoledactylus, Hall). B five, of irregular form and 
size. five, the right posterior one horizontally divided. Ventral tube long 
and narrow, and resting upon the sloping upper face of the inferradial. Arms 
non-pinnulate, branching. Column evolute at its upper end, and more or less 
round ; involute and crescent-shaped toward the terminal end, with large cirri 
springing from the two horns of the crescent; section sharply pentagonal. 
Silurian ; North America and Europe. 
Family 4. Belemnocrinidae. Wachsmuth and Springer. 
Base monocyclic; cylindrical to ovoid. It is composed of five large, elongate, 
irregular pieces, and is pierced by a small canal which widens slightly at the upper 
enl. Radials five, quadrangular, and separated posteriorly by a narrow IRA. 
Ventral sac large, composed of hexagonal plates, the angles of which are perforated. 
Arms long, giving off armlets alternately at intervals. Column round or pentagonal ; 
in the latter case having its angles radially directed. Cirri, when present, interradial 
in position. Sub-Carboniferous. 
Belemnocrinus, White. Burlington Group ; Mississippi Valley. 
Family 5. Catillocrinidae. Wachsmuth and Springer. 
Base monocyclic; dorsal cup saucer-shaped ; general symmetry of the calyx 
greatly disturbed. Basals irregular in form, their number unknown ; radials still 
more irregular both in form and in size. Most of the arms given off from two of 
the radials, which are sometimes five or six times larger than the other three ; they 
are simple, quadrangular, and rest within small sockets directly upon the radials. 
Anal plates wanting. Ventral tube heavy, composed of very long, longitudinally 
arranged crescent-shaped pieces, and supported directly by the radials ; it exhibits a 
wide open groove along the anterior side, which probably was. covered by small 
delicute plates. Devonian and Sub-Carboniferous. 
Catillocrinus, Troost. Crown, when the arms are closed, elongate, cylindrical. 
Calyx basin-shaped, concave at the base, truncate at its upper margin. Basal 
disk small. five; those of the two anterolateral rays fully six times as wide 
as the others, and expanding upwards, so as to encroach upon the smaller ones. 
The larger & support twelve to sixteen arms; the smaller ones rarely more 
than one each. Sub-Carboniferous ; North America. 
Mycocrinus, Schultze. Dorsal cup mushroom-shaped. Plates massive, 
irregular, and without ornamentation. B two (according to Schultze), one of 
