998 ME. F. A. BATHER ON UINTACEINTTS. [DeC. 17, 



and apparently by Schlueter (4), who, however, cleverly shirked 

 giving a definite reply, this opinion demands respectful considera- 

 tion. The opinion will be more acceptable if Onychocrinus be 

 substituted for Forbesiocrinus. Por in Onychocrinus one finds what 

 does not occur in Forhesiocriniis, namely a differentiation of the 

 arms into two main branches, with a tendency for the armlets 

 to be reduced to the size and regularity of pinnules. This 

 tendency is most obvious in the species for which E. R. Eowley ^ 

 proposed two generic names in a single paper, viz., Aristocrinus, or 

 Oallawaycrinus, concavits. Considering the extreme difficulty that 

 the most acute palaeontologists have met with in distinguishing 

 the genera IchtJiyocrinus, Taa'ocrinus, Forbesiocrinus, Onychocrinus, 

 and their allies, considering the impossibility of deciding such a 

 question with the assistance of the comparatively few specimens 

 or species in the British Museum, and considering the confused 

 nature of the large and scattered literature, I would not, on the 

 slight evidence offered by Mr. Eowley, venture to pass any 

 criticism on his action other than that the name Arisiocrhius, or 

 " the best crinoid," is singularly inappropriate. Names and minor 

 differences apart, we find in this group of forms many species 

 with small and disappearing infrabasals, with interbrachials forming 

 a flexible union between the rays, with occasional interdistichals, 

 with the proximal primibrachs and secundibracbs broad-backed 

 thin plates A'ery like those of Uintacrinus, with an axial canal 

 differentiated in at least the more distal brachials, with a flexible 

 tegmen, and with flexible arms and cup ; and some species with a 

 distichal and sub-pinnulate arm-structure, and with two primi- 

 brachs in each ray. In all these features, then, there is a note- 

 worthy resemblance ; but a closer inspection will reveal many 

 important points of difference. The species to which reference 

 has been made have an anal area distinct in the cup, such as there 

 is no trace of in Uintacrinus. This, however, might well disappear 

 in course of evolution, especially in a free-swimming form, just as 

 it has disappeared in Encrinus and in Antedon, although un- 

 doubtedly present in the ancestors of those two genera. It is 

 more important to notice that the interradially situate plates of 

 the Ichthyocrinidae are all of them true interbrachial plates of the 

 secondary system ; they are none of them modified pinnules. 

 Indeed the pinnules are in no case advanced to such a stage that 

 they could coalesce as in Uintacrinus. The most one can say is, 

 that in some species of Ichthyocrinus the brachials seem to have 

 been united laterally. Again, there are no traces of syzygial union 

 in the arms of the Ichthyocrinidae. Indeed the arms are so much 

 less differentiated, even in Onychocrinus, than they are in Uinta- 

 crinus, that if one supposes any links between the two forms, one 

 must suppose a very long chain of them. But of this chain, not 

 one link is known. Therefore, though I admit the force of the 



1 " Description of a new Genus and five new Species of Fossils from the 

 Devonian and Sub-Carboniferous Bocks of Missouri," Amer. Geol. xvi. pp. 217- 

 223 (Oct. 1895). 



