ECHINODERMATA—CRINOIDEA. 503 



This T-piece is low, wide and sometimes very small. The anal 

 tube is supported by the T-piece and the right anterior and right 

 posterior inferradials, not touching the two large, simple R. Arms 

 three, rising only from the three anterior R, and composed of single 

 joints which are usually as long as wide and grooved ventrally. 



Remarkable especially in the connection of B and R by muscles 

 and ligaments instead of by suture, allowing the calyx to bend 

 along this articular line. Siluric-Devonic. 



12. C. radicula Ringueberg. Siluric. 

 Calyx compressed cylindrical. Arms three — one dorsal and two 



lateral, the lateral arms bifurcating. Basal plate narrow, triangu- 

 lar. All arms branching. Calyx one third of an inch high. 

 Niagaran (Rochester shale) of New York. 



IX. Halysiocrinus (Ulrich) Bather. 

 Similar to Calceocrinus, but the T-piece is either obsolete or con- 

 cealed, leaving the tube supported by the right posterior and right 

 anterior lateral inferradials and abutting against the anterior and 

 left posterior R. Likewise the simple anterior R of Calceocrinus 

 is here compound, the two parts separated by the right and left 

 antero-lateral R. Mississippic. 



13. H. ventricosus Hall. Mississippic. 

 Resembles H. hradleyi, but is slightly smaller, the greatest breadth 



Fig, 1815. Halysiocrinus bradleyi ; FiG. l8l6. Carabocrinus geometricuSy 

 dorsal and anterior view, side view of base, X 4' (After Hudson. ) 

 X Vi' (After Meek and Worthen. ) 



of the calyx is toward the summit instead of the base and the arms 

 bifurcate less frequently. (Type of genus.) 

 Burlington of Missouri and Iowa. 



