214 ECHINODEEMATA— PELMATOZOA phylum iv 



fused plates very rarely entering the stem articulation. The posterior and 

 right anterior basals bounded for some distance by the large R. T-plate 

 separated from the large simple R by the right posterior and right anterior 

 radials ; it is low, wide, and occasionally very small. Tube supported by 

 the T-piece and the two inferradials to the right, but not touching the two 

 large simple radials. Arms three. Silurian and Devonian ; Europe and 

 America. Type, D. clarus (Hall). 



Halysiocrinus Ulrich em. Bather. B as in the preceding, but the fused 

 posterior and right anterior ones never entering into the stem articulation. 

 T-piece either obsolete or concealed between the right posterior and right 

 anterior inferradials, and the two large radials in the stem articulation. 

 Tube supported by the inferradials to the right, which are in contact, and 

 abutting by its lower corners on the two large simple R. Arms three. Bur- 

 lington and Keokuk Groups ; Mississippi Valley. Type, H. dadylus (Hall). 



Family 5. Oatillocrinidae Wachsmuth and Springer. 



Base monocyclic ; dorsal cup low and broad ; general symmetry of the calyx 

 greatly disturbed. Basals more or less fused, their number doubtful ; radials still 

 more irregulär bofh 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, qnadrangular, non-pinnulate, and rest within small sockets directly upon 

 the radials. Anal plates wanting. Anal 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 delicate plates. Devonian and Lower Carboniferous. 



Mycocrinus Schultze. Dorsal cup mushroom-shaped. Plates massive, 

 irregulär, and without ornamentation. B two (according to Schultze), one of 

 them twice as large as the other, and the two forming a knob-like body. R 

 five, their inner edges resting upon the angular margin of the basal disk ; they 

 spread broadly outward from the B, extending far beyond them. The two 

 larger R separated at the posterior side by two equal smaller plates ; and at 

 the anterior side by a single plate having a quite narrow upper face. M. 

 boletus Schultze has apparently fif teen arms, their structure unknown. Middle 

 Devonian ; Eifel. , 



Catillocrinus Shumard ex Troost (Nematocrinus M. and W.). Crown, when 

 the arms are closed, elongate, cylindrical. Dorsal cup basin-shaped, concave at 

 the base, truncate at its upper margin. Basal disk small. R five; those 

 of the two antero-lateral rays fully six times as wide as the others, and 

 expanding upwards, so as to encroach upon the smaller ones. The larger R 

 Support each twelve to sixteen arms ; the smaller ones rarely more than one 

 each. Lower Carboniferous ; North America. 



Family 6. Belemnocrinidae Wachsmuth and Springer. 



Base monocyclic ; cylindrical to ovoid. B is composed of five large, elongate, 

 irregulär pieces, and is pierced by a small canal which widens slightly at the upper 

 end. Radials five, quadrangidar, and separated posteriorly by a narrow anal. 

 Ventral sac large, composed of hexagonal plates, the angles of which are perforated. 



