188 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



Bhodocrinus. 



Fiii. 2«S. 

 Analysis of calyx (after W. 

 aud Sp.)- 



uiiiserial ; from ten to twenty, and branching further. Otherwise simihir to 

 Archaeocrinus. Ordovician ; North America and England. 



Archaeocrinus W. and Sp. Calyx obovate to hemispherical ; base usually 

 concave or invaginate. IBB small. Brachials to at least second order in- 

 corporated in the calyx. Arms biserial, usually ten at their origin and 



branching beyond. Anal interradius 

 slightly distinguished by an additional 

 plate in second range ; iBr numerous. 

 Anus without a tube. Ordovician ; Canada 

 and Kentucky. 



Diabolocrinus W. and Sp. Calyx de- 

 pressed globose. Anus at end of a tube. 

 First regular interbrachial frequently 

 surrounded by supplementary plates. 

 Ordovician ; Tennessee. 



Deocrinus and Hercocrinus Hudson. 

 Ordovician ; Canada. 



Bhodocrimis J. S. Miller (Acanthocrinus 

 Roemer) (Fig. 285). Calyx globose, 

 usually small and delicate, with concave 

 base, and constricted at the tegmen. 

 Arms becoming free at the distichals, and 

 branching ; biserial, either directly from 

 the calyx up, or only from the last bi- 

 furcation. Anal side frequently, but not always, distinct from the regular 

 interbrachial areas, by interposition of an extra plate in the second range. 

 Devonian to Lower Carbon- 

 iferous (Keokuk Gr.); North 

 America, England, Belgium, 

 Germany. 



Gilbertsocrimis Phillips 

 (Goniasteroidocrinus Lyon and 

 Cass.; Ollacrinus Cumberland 

 nomen nudum). Calyx below 

 the arm-regions like that of 

 Bhodocrinus, but usually 

 larger, expanding at the 

 tegmen instead of constrict- 

 ing, and distinguished especi- 

 ally by large tubular ap- 

 pendages extending outward 

 and downward from the 

 margin of the tegmen, and 

 overhanging the arm bases. 

 These appendages are formed 

 of rows of cylindrical plates, 

 pierced to their full length 

 by a central canal ; they are 

 primarily ten in number, in some species free, and in some fused by their 

 outer margins to those of adjacent rays. Arms small, delicate, biserial, given 



Fin. 286. 

 Uhipldocrinus crenatua (Goklf.). Uevouian ; Gerolstein, Eifel. 

 A, Perfect crown, of the natural size (after Schnltze). 7i, Tegmen, 

 with eccentric anus. C, Interior view of the base, showing the five 

 ll'Ji, two of Uie basals and one radial. /), Column. A', Face of stem- 

 joint. 



