220 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



dichotomous, and freely branching. Posterior oral usually a madreporite ; other 

 orals often largely hidden hy encroaching tegmenal plates. Infrahasals five, excep- 

 tionally tliree. Stern usually round. Silurian to Lower Carbon iferous. 



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

 short, 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 



a, Gissocrimis arthriticus Phill. Silurian ; Got- 

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

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

 lateral aspect of the arms (enlarged). 



m-^CT-^tTXTX: 



Fio. 318. 



Cyatlwcrlmis. Analysis of dorsal 

 cup (after Bather). 



Fig. 319. 



a, Cyathocrinus longimanus Ang. Silurian ; 

 Gotland. Crown of the natural size (after 

 Angelin) ; />, C. ramosus Ang. Portion of an 

 arm viewed from the side ; c, Ventral aspect of 

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

 Carboniferous ; Burlington, Iowa. Tegmen 

 perfectly preserved ; e, The same after removal 

 of the covering pieces and orals (after Meek 

 and Worthen). 



and rounded, or long with a valvulär 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. Kadial 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, streng, 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. 



