204 ECHINODERMATA— PELMATOZOA phylum iv 



rhombic, obliquely below r.post.R. IBr oiie to four. Silurian ; Gotland, 

 England, and North America (Niagara of western area and of New York). 



Nipterocriniis Wachsmuth, in Meek and Worthen. Similar to Pycmsaccus, 

 but without BA or anal x, and with infrabasals fused to one. The last 

 survivor of this family. Lower Burlington to Keokuk ; Mississippian area, 

 North America. 



Family 2. Sagenocrinidae Springer. 



Infrabasals ahutting on dorsal side of basals, low and flat, taking Utile part in 

 calyx wall. Crown usually large, elongate, expaiiding above the radials. Rays 

 above radials partly or wJiolly separated all around. Silurian to Lower 

 Carboniferous. 



Temnocrinus Springer. Arms dichotomous. Anals and iBr only in lower 

 part of interradial areas ; anals more than one abreast. BA in form of B 

 under r.post.R. Anal x separating BB and touching post.B. IBr two. 

 Type, Taxocrinus tuberculatus Miller. Silurian ; England, (?) North America. 



Meristocrinus Springer. Similar to Temnocrinus, but with anal x followed 

 by other plates in series, and IBr three. Type, Taxocrinus loveni Angelin. 

 Silurian ; Gotland. 



Sagenocrinus Austin. Arms dichotomous. Anal and iBr areas filled with 

 solid plates. BA obliquely below r.post.R, usually between BB, and not 

 touching r.ant.R. IBr two. Silurian ; England, Gotland, and North 

 America (Western Niagara). 



Lithocrinus W. and Sp. (Forbesiocrinus Ang. non Kon.). No BA. Arms 

 heterotomous, with ten main trunks bearing branching ramules. iBr well 

 developed in lower part of areas. IBr two. Type, Forbesiocrinus divaricatus 

 Ang. Silurian; Gotland. 



Forbesiocrinus Koninck and Lehon. No BA. Arms dichotomous. iBr 

 usually numerous, Alling the areas with solid plates. IBr three, except in 

 F. agassizi, which has two. The culmination of this family. Lower Carboni- 

 ferous (Lower Burlington to Warsaw) ; Belgium. Also Mississippian area, 

 North America. 



Family 3. Ichthyocrinidae Wachsmuth and Springer (restr.). 



Infrabasals wholly witliin the ring of basals, concealed by the column, 

 sometimes disappearing by resorption. Crown usually elongate, 

 expanding above radials, but often infolding distally. Arms 

 usually closely abutting or interlocking. Silurian to Lower 

 Carboniferous. 



a. Rays in contact except between posterior radials when separated 

 by anal x. 



Ichthyocrinus Conrad (Fig. 305). Arms dichotomous, 



Fig. 305. closely interlocking, and infolding. BA in form of B under 



Ichthyocrinus laevis r.post.R. No anal, üosterior basal not difFerentiated. IBr 



crown. Silurian (Xia- two. Silurian ; Gotland, England and North America (New 



port, New' York (after York and Western Niagara area). 



^^^^^- Clidochirus Ang. Similar to Ichthyocrinus, but with 



posterior basal difFerentiated, supporting anal x alone, or followed by others. 



