222 



ECHINODEKMATA— PELMATOZOA 



PHYLUM 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 Eoeiuer (emend. Waclism. and Springer). 



Dicydic. Tegmen composed of undifferentiated ■plates, without identifiable orals 

 or amhulacrals ; more or less extended into a ventral sac, with amis heloiv the distal 

 end on the anterior side. Union of radials with first brachials usually by complete 

 muscular articulation, upon straight facets as loide as the radial, with fossae, paired 

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



form). Arms pinnulate, mostly dichotomous. Infra- 

 basals five, exceptionally three, or coalesced into one. 

 Stem usually with cirri. Devonian to Permian. 



Subfamily A. Poteriocrininae. 



Radianal in oblique position. Anal x usually in 

 line with radials. Arins iisually uniserial, tending to 

 biserial in later genera ; dichotomous or heterotomous. 

 Infrabasals usually five. Crown usually elongate, 

 expanding upward. Stem 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 arras. Stem 

 usually round, without 

 cirri, at least in upper 

 part. (?) Devonian and 

 Lower Carboniferous 

 (Keokuk) ; Euroi:)e and 

 North America. 



The Devonian species 

 referred to this genus are 

 probably Farisocrinus ; 

 without the arms being 



Fig. 321. 



Paohyl OCT inns unicus Hall. Lower 

 Carboniferous (Keokuk Group) ; Craw- 

 fonlsvillr, Indiana. Natural size. 



Fio. 322. 



Pachylocrinus sp. Analysis of dorsal 

 cup. a, Anal x; a', Right tube-i)late ; 

 /(, liasals ; (7>, Infrabasals ; -/•, Right and 

 left jjosterior radials ; ra, Radianal. 



Pig. 323. 

 Pachylocrimia acqualis Hall. 

 Lower Carboniferous (Keokuk 

 Group) ; Crawfordsville, Ind. 

 Complete crown from posterior 

 side, showing base of ventral sac 

 and mode of arm-branching. 



preserved tliis cannot be 

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

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



