210 Air. F. A. Bather on Brltisli Fossil CrinoUh : 



it is separate in tlie closely allied C. acinotuhus ; while it is 

 separate in some individuals of C. striolatus from Gotland 

 bnt not in others. Consequently it seems advisable for the 

 present to retain both Silurian and Carboniferous species in 

 one genus — Cyathocrinus — with the following 



Generic Diagnosis. 



IBB 5, equal, pentagonal. BB 5, hexagonal except post. 

 B, which is heptagonal and supports x. RR 5, shield-shaped, 

 with facet circular or elliptical in outline, and occuj)ying from 

 less than ^ to | width of R. x tetragonal to hexagonal, in 

 line with RR, and about | width of R. Arms long, simple, 

 dichotomizing regularly several times ; covering-plates alter- 

 nating, in from 1 to 4 (or 5 ?) rows on either side. Ventral 

 sac composed of usually hexagonal plates, either smootli or 

 slightly folded. Tegmen consolidated by deltoids. Madre- 

 porite distinct. 



Desceiption of the Genus. 



Dorsal Cup cyathiform ; with sides convex, straight or 

 convexo-concave ; with plates ]jlane or tumid ; surface 

 smooth, shagreened, or slightly lidged either radiately or 

 concentrically. No pronounced axial folding. 



]BB 5 ; pentagonal ; lying at very various angles to stem, 

 and varying veiy greatly in height. 



BB 5 ; hexagonal, except post.B, which is heptagonal. 

 These also vary much in their proportions, but are usually 

 large. 



RR 5 ; of normal outline ; as large as or larger than BB. 

 Articular facet from a little less than i to f width of phite, 

 usually about ^ ; circular or elliptical in outline ; directed 

 outwards and upwards at very various angles ; axial canal 

 may or may not be se])arated from the ventral groove by 

 stereom. Radial processes curve upwards and inwards to the 

 deltoids. 



Arms non-])innulate, dicbotomous ; usually long and 

 branching from 5 to 7 times (in Silurian species at least) ; 

 with more ossicles in each series towards the inner side of 

 each dichotom. Rather stout, not tapering much, and with 

 short ossicles (in Silurian species) ; or fine, tapering, with 

 long ossicles (in Carboniferous species). Covering-jdates 

 well developed; either as solid, alternating series, or in rows 

 of 2 to 5 (?) dee]) on either side of ventral groove. 



1 Br from 1 to about 8 : the nundjer often varies LLieatlv in 



