UINTACRINUS: ITS STRUCTURE AND RELATIONS. 23 



homologies are therefore doubtful, as its structure and position permit 

 it to represent either a relic of a stem, or a fused infrabasal circlet, or 

 even, as some would have it, an additional element to which the term 

 ' dorsocentral ' might be strictly applicable." ^ 



Further on, when comparing this genus with Marsupites and Saccocoma 

 (p. 996), he says : '^ Saccocoma has a cup of nothing but radials ; Marsupites 

 has radials, basals, and infrabasals ; Ui7itacrinus has no infrabasals, but 

 in addition to its basals and radials, has brachials, interbrachials, inter- 

 distichials, pinnulars, and interpinnulars, all helping to compose its dorsal 

 cup. ... It is also noteworthy that each of these very differently con- 

 stituted cups resembles the others in one curious feature, namely : the 

 presence of a central, pentagonal, apical plate. One may say, if one 

 choose, that in Saccocoma this represents the fused basals, and in Uintacriniis, 

 the fused infrabasals ; 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 dis- 

 tal 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." 



Summing up, he says (p. 997) : '^ The essentials of structure in Uintacrinus 

 appear thus to be : 5 basals, 5 radials, 5 arms branching once," etc. This is 

 a distinctly monocyclic base ; and in seeking the derivation of Uintacrinus 

 Mr. Bather elsewhere (p. 997) says : — 



'^ Turning to the Inadunata, we have to choose between monocyclic and 

 pseudo-monocyclic forms; since had the immediate progenitors of Uintacri- 

 nus well-developed infrabasals, one must suppose that these would have 

 been retained and utilized to expand the walls of the cup, as in Marsupites'' 



In these observations Bather was perfectly justified by the material 

 before him, and by the statements of previous waiters. Hill t says : " In 

 place of the sub-basal plates of the stemmed Crinoids, there is a small, five- 

 sided centrodorsal plate, around which are grouped five pentagonal basals." 



It now appears, however, thvat while the above description of the base is 

 correct for many of the specimens, it is by no means uniformly the case. 

 In a large proportion of them there is a distinct and well-developed circlet 

 of infrabasals surrounding the centrale — thus producing a dicyclic base. 



* Proc. ZooJ. Soc. London, 1895, p. 979. 



+ Kansas University Quarterly, 1894, Vol. 111., No. 1, p. 20. 



