1895.] MK. F. A. BATHEE ON UXNTACEINTJS. 997 



both test and arms, are obyious points that have already 

 been alkided to. It is also noteworthy that each of these 

 very differently constituted cups resembles the others in one 

 curious feature, namely, the presence of a central, pentagonal, 

 apical plate. One may say, if one chooses, that in Saccocoma this 

 represents the fused basals, and in Uintacrinus the fused infra- 

 basals ; but in Marsupites it must be something else. Or one may 

 say that in each case it is the same element, be it the proximal 

 stem-ossicle (which some erroneously call " centrodorsal "), or the 

 distal stem-ossicle (which some, seeking an homology, have called 

 " dorso-central "), or perhaps a new plate altogether, a simple 

 supplementary plate developed to fill up the gap left by the 

 disappearance of the stem. One might argiie for ever : there is 

 no evidence. The one obvious fact is that such a central plate is 

 found in three very different forms, all of which were free- 

 SAvimming, and unlike all other crinoids in showing absolutely 

 no trace of a stem. It is therefore not safe to ascribe to the 

 central plate any morphological significance, or to give it any name 

 other than " centrale." 



The large size of the body is produced in Marsupites, and stiU 

 more in Saccocoma, by the largeness of the plates ; in Uintacrintts 

 it is produced by the incorporation of many brachials, inter- 

 brachials, &c. into the dorsal cup. The large size being probably 

 a secondary character, it is not fair to argue that the ancestors of 

 Uintacrimis had so many plates in the dorsal cup ; although we 

 must infer that they were forms that had a tendency to this mode 

 of enlargement of the cup. 



The essentials of stnicture in Uintacrinvs appear thus to be : 

 5 basals ; 5 radials ; 5 arms, branching once ; the two primibrachs, 

 at least, united by interbrachial ; pinnules borne by secundibrachs, 

 beginning with IIBr., ; a tendency for proximal pinnules to 

 coalesce ; an axial canal separated from the ventral groove of the 

 brachials. 



As claimants to provide an ancestor for Uintacrinus the 

 Camerata, notA^-ith standing the superficial resemblance in the cup 

 of many of them to this genus, must at once be put out of court 

 as having no separate axial canal in the arms. The flexible tegmen 

 of Uintacrinus is also removed from the Camerate type. Indeed, 

 so far as I am aware, Jaekel (10) is the only writer of repute that 

 has endeavoured to find the ancestor of Uintacrinus in this order. 

 The Ehodocrinidse, however, which are the forms he fixes on, are 

 far removed fi'om Uintacrinus, in the possession of branched, 

 biserial arms, and interradials resting on the basals. 



This leaves, among Palaeozoic crinoids, from which one pre- 

 sumes that Mesozoic crinoids are descended, the Inadunata and 

 the Ichthyocrinacea (=ArticLdata, "W. & Sp., Flexibilia, Zittel). 



Most if not all of those palseontologists that have attempted an 

 answer have decided in favour of the Ichthyocrinacea, usually 

 pitching on Forhesiocrinus as their example of a similar form. Held, 

 as it has been, by Zittel (5 and 11), Neumayr (6), Carpenter (7), 



