210 Mr. F. A. Bather on British Fossil Crinoids : 
it is separate in the closely allied C. actnotubus ; while it 1s 
separate in some individuals of QO, striolatus from Gotland 
but 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. BB5, hexagonal except post. 
B, which is heptagonal and supports 2. RR 5, shield-shaped, 
with facet circular or elliptical in outline, and occupying from 
less than } to 3 width of R. a tetragonal to hexagonal, in 
line with RR, and about 3 width of R. Arms long, simple, 
dichotomizing regularly several times ; covering-plates alter- 
nating, in from 1 to 4 (or 5?) rows oneither side. Ventral 
sac composed of usually hexagonal plates, either smooth or 
slightly folded. 'Tegmen consolidated by deltoids. Madre- 
porite distinct. 
DESCRIPTION OF THE GENUS. 
Dorsal Cup cyathiform; with sides convex, straight or 
convexo-concave; with plates plane or tumid; surface 
smooth, shagreened, or slightly ridged either radiately or 
concentrically. No pronounced axial folding. 
IBB 5; pentagonal; lying at very various angles to stem, 
and varying very greatly im 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 4 to 2 width of plate, 
usually about $3 circular or elliptical in outline; directed 
outwards and upwards at very various angles; axial canal 
may or may not be separated from the ventral groove by 
stereom. Radial processes curve upwards and inwards to the 
deltoids. 
Arms non-pinnulate, dichotomous; 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-plates 
well developed; either as solid, alternating series, or in rows 
of 2 to 5(?) deep on either side of ventral groove. 
i Br from 1 to.about 8: the number often varies greatly in 
