222 



ECHINODERMATA— PELMATOZOA 



PHYLÜM IV 



Maragnicrinus Whijtfield. From the same locality and horizon as the 

 last; differing from it in having narrower arm facets, the arms regularly 

 dichotomous, branching once, and the rami bearing pinnules directly. 



Family 11. Poteriocrinidae Eoemer (emend. Wachsm. and Springer). 



Dicydic. Tegmen cornposed of undifferentiated plates, without identifiable orals 

 or amhulacrals ; more or less extended into a ventral sac, with anus helow the distal 

 end on the anterior side. Union of radials with first hrachials usualhj by 

 muscular articulation, upon straight facets as wide as the radial^ with fossae, 

 muscles and ligaments, and transverse ridge (exception in Poteriocrinus, a transition 



form). Arms pinnulate, mostly dichotomous. Infra- 

 hasals five, exceptionally three, or coalesced into one. 

 Stern usually with cirri. Devonian to Permian. 



Subfamily A. Poteriocrininae. 



Radianal in oblique position. Anal x usually in 

 line with radials. Arms usually uniserial, tending to 

 biserial in later genera ; dichotomous or heterotomous. 

 Infrabasals usually five. Crown usually elongate, 

 expanding upward. Stern usually round, occasionally 



pentagonal. Devonian to 

 Upper Carboniferous. 



Poteriocrinus Miller. 

 Radial facet usually 

 curved, less than width 

 of B, with imperfect or 

 no transverse ridge. 

 Arms dichotomous, 

 branching frequently. 

 Ventral sac large and 

 long, usually rising be- 

 yond the arms. Stem 

 usually round, without 

 cirri, at least in upper 

 part. (?) Devonian and 

 Lower Carboniferous 

 (Keokuk) ; Europe and 

 North America. 



Fig. 321. 



Pachylocrinus unicus Hall. Lower 

 Carboniferous (Keokuk Group) ; Craw- 

 fordsville, Indiana. Natural size. 



Fig. 322. 



Pachylocrinus sp. Analysis of dorsal 

 cup. a, Anal x; ai, Riglit tube-plate ; 

 h, Basais ; ib, Infrabasals ; r, Right and 

 left posterior radials ; ra, Radianal. 



The Devonian species 



referred to this genus are 



probably Parisocrinus ; 



without the arms being 



this cannot be 



Fig. 323. 

 Pachylocrinus aequalis Hall. 

 Lower Carboniferous (Keokuk 



Group); Crawfordsville, Ind. 



Complete crown from posterior T»rp«prvprl 

 side, showing base of ventral sac U'^^^^y^^ ^ 



andmodeofarm-branching. certainly determined. The 



genus lacks the complete 

 muscular articulation characteristic of the family, but is otherwise typical. 



Pachylocrinus Wachsmuth and Springer {Scaphiocrinus auctt., non Hall = 

 Graphiocrinus ; Hydriocrinus Trautschold ; Abrotocrinus M. and G.) (Figs. 269, 

 321-3). Radial facets of this and all succeeding genera normal for the family. 



