VIII. Cyathocrinus. 209 
separate Spherocrinus from Cyathocrinus ; still this was not 
on account of any differences in the structure of the cup, but 
merely because the axial canal in the radials was separated by 
stereom from the ventral groove. ‘l’o the question whether 
this character is of generic importance we shall return imme- 
diately ; for the present it is enough to state that the descrip- 
tion of Poteriocrinus geometricus given by Miiller and Schultze 
is proved correct by a large number of specimens in the 
British Museum. So long as the arms of this species are 
unknown one cannot definitely say to which genus it belongs; 
it would probably be safer to place it in Parisocrinus, but 
we may be quite certain that it has nothing to do with 
Cyathocrinus. 
A single species, hitherto undescribed, which may be 
regarded by many as a Cyathocrinus, has been separated 
therefrom and made the type of a new genus, under the name 
Mastigocrinus loreus. ‘The reasons for this have been so 
fully given in the preceding paper (anted, p. 200) that it 
would be waste of space to repeat them here. Suffice it to 
say that no Cyathocrinus has yet been found with a ventral 
sac, a teemen or a stem like those of Mastigocrinus. 
Wachsmuth and Springer (Rev. III. 326; Proc. 1886, 
p- 150) have stated that the possession of a separate axial 
canal by the radials is a structure that “ occurs exclusively in 
species from the Silurian and Upper Devonian, never in the 
Carboniferous, neither in Cyathocrinus nor other genera.” 
“ Whether,” they continue, “ all species of Cyathocrinus from 
Gothland and Dudley possess this structure, cannot be ascer- 
tained from the figures, but if they do, it may form the basis 
of a separation which seems to us very desirable.” Now, 
even if we were safe in accepting this remarkably broad and 
dogmatic, though not very clear, statement, intermediate 
forms might still occur in the Lower and Middle Devonian, 
Even if they did not, so small a point would hardly be 
enough to differentiate two genera; for it is no rare thing to 
find the axial canal separate in one species of a genus, in one 
individual of a species, or in the earlier brachials of an indi- 
vidual, while it is merely a tongue from the ventral groove 
in others *, Moreover there do not appear to be any other 
constant or decided differences between the Carboniferous 
species of Cyathocrinus and such typical Silurian species as 
C. oe C. ramosus, and C. visbycensis. As a matter 
of fact, however, even this difference does not exist, for the 
axial canal is not separate in the Silurian C. vadlatus, although 
* See “ Brit. Foss. Crin.—V. Botryocrinus,” Ann. & Mag. Nat. Hist. 
ser. 6, vol. vii. p. 392, May 1891. 
