220 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



dicJiotomo'US, and freely branching. Posterior oral usually a madreporite : other 

 orals often largely hidden by encroaching tegmenal plates. Infrabascds five, excep- 

 tionally three. Stem usually round. Silurian to Lower Carboniferous. 



Gissocrinus Ang. (Fig. 317). IB three. Anal tube compressed, its plates 

 sliort, wide and folded. Distal margin of brachials usually project. Silurian ; 

 Gotland, England and North America. 



Cyathocrinus Miller (Figs. 318, 319). Infrabasals five. Anal tube short 



Fio. 317. 



a, Gisf-ocrinits arthriticns Phill. Silurian ; Got- 

 land. Crown of the uatnral size (after Angelin) ; 

 h, G. imnctuosus Ang. Tegmen ; c, Ventral and 

 lateral aspect of the arms (enlarged). 



r ft« 



m^oo-tTt:i 



Fic. 318. 



C'yatliurrinn.s. Analysis of dorsal 

 cup (after Bather). 



Fig. 319. 



a, Cyathocrinus longimanus Ang. Silnrian ; 

 Gotland, Crown of the natural size (after 

 Angelin); h, C. ramosus Ang. Portion of an 

 arm viewed from the side ; c, Ventral aspect of 

 same (enlarged); d, C. malvaceiis Hall. Lower 

 Carboniferous ; Burlington, Iowa. Tegnien 

 perfectly preserved : e, The same after removal 

 of the covering pieces and orals (after Meek 

 and Worthen). 



and rounded, or long with a valvular pyramid at distal end ; its plates more 

 or less hexagonal, not transversely elongate, nor much folded. Arms branch- 

 ing as many as five to seven times. Radial facets horse-shoe shaped, directed 

 outward, with occasional incipient transverse ridge. Ambulacral covering 

 plates well developed, regularly alternating, or modified so as to resemble 

 budding pinnules. Stem round, strong, short, apparently without cirri. A 

 well-known and widely distributed genus, occurring from the Silurian to 

 Lower Carboniferous (Warsaw) ; Europe and America. 



Mastigocrinus Bather. Like Cyathocrinus in the structure of the calyx, 



