VIII. Cijathorrinns. 201) 



separate Sphcerocrinus from Cifdtliocrinus ; still this was not 

 on account of any diflfcrcnccs in the structure of the cup, but 

 merely because the axial canal in the radials was separated by 

 stercom from the ventral groove. To 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 Potei-iocrinus qeonietn'cus g'lvenhy 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 Pxrisocrinus, but 

 we may be quite certain that it has nothing to do with 

 C)/athocrini(s. 



A single species, hitherto undescribed, which may be 

 regarded by many as a Ci/athocrinus, 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 [anteh, p. 200) that it 

 would be waste of space to repeat them here. Suffice it to 

 say that no CyatJwcrinus has yet been found with a ventral 

 sac, a tegmen or a stem like those of Mastigocriium. 



Wachsmuth and Springer (Rev. III. 32G ; 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 

 (Jarboniferous, neither in Cyatlwcrinus nor other genera." 

 " Whether," they continue, " all species of Cyathocriaus froni 

 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 wiiich 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 mio'ht still occur in the Lower and JMiddle Devonian. 

 Even if they did not, so small a point would hardly be 

 enough to ditferentiate 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 diflerences between the Carboniferous 

 species of Cyatlwcrinus and such typical Silurian species as 

 (]. acinotuhus^ C. rnnicsus^ 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 G. vallatuSj although 



* See "Brit. Foss. Criu.— V. Bofri/ocnnxs,'" Aun. .t Maq-. Xat. Hist, 

 ser. 6, vol. vii. p. 392, May 1891. 



