1895.] MB."f . A. BATHER Olf UINTACEINTJS. 999 



arguments of those eminent authorities who, with Neumayr (6), 

 " regard it as most probable that Uintacrinus is a last straggler of 

 the Ichthyocrinidse," yet I cannot but consider the counter- 

 arguments, here first definitely stated, as of even greater weight. 

 One may also add the fact that none of the known Flexibilia show 

 that predilection for a free mode of Ufe that is so common in the 

 order next to be considered. 



Turning to the Inadxmata, we have to choose between mono- 

 cyclic and pseudo-monocyclic forms ; since, had the immediate 

 progenitors of Uintacrinus well developed infrabasals, one must 

 suppose that these would have been retained and utilized to expand 

 the walls of the cup, as in Marsnpites. 



Among Inadunata monocyclica choice is at the outset limited 

 to those genera whose symmetry is not disturbed either by the 

 transverse bisection of certain radials or by the greater develop- 

 ment of certain other radials. From these more symmetrical 

 forms, again, must be removed those that have simple iinbranched 

 arms, such as Hoplocnnus, Bybocrinus, SymbatJiocrinus, and Cupresso- 

 crinus. locrinus, with its dichotomus, non-pinnulate arms, is also 

 X)at of the question ; while one need hardly mention such undeve- 

 loped genera as Gasterocoma, Lac/eniocrinus, and Allagecnmis. 

 Thus Belemnocrimis, if correctly placed here, is the only genus 

 remaining; in its bifurcate, sub-pinnulate ai-ms, richly provided 

 with syzygies, and in the structure of its cup, it certainly presents 

 more resemblance to Uintacrinus than do any of the other genera ; 

 but in its large anal tube, and in the entire absence of any plates 

 binding together the brachials, it is still far removed from our 

 genus. 



The field of choice is now narrowed down to the Inadxmata 

 dicyclica and their descendants in the Mesozoic era, the Canali- 

 culata. The earlier fistulate forms, with their asymmetrical anal 

 areas, may be at once set aside ; so may all genera with many- 

 branched arms, whether pinnulate or non-pinnulate. Thus we are 

 restricted to such genera as Erisocrinus, Stemmatocrinus, Encrinus, 

 Dadocriniis, and some species of Pentacrinidse. At first sight 

 there appears mighty little resemblance between these and Uinta- 

 crinus ; so little that no one has ever dreamed of mentioning them 

 in this connection. Yet it is here, and here only, that we find 

 those essentials of structure that have been proved requisite in 

 the ancestors of Uintacrinus. A large number of these genera 

 agree in the possession of 5 basals, 5 radials, two primibrachs in 

 each radius, arms bifurcating once, bearing pinnules, and with a 

 separate axial canal. The earlier genera have distinct infrabasals ; 

 but the later genera are pseudo-monocyclic, the infrabasals being 

 either absorbed or hidden in the adult, and occasionally fused with 

 one another. It has already been suggested that Uintacrinus was 

 more likely to be descended from a pseudo-monocycHc than from a 

 dicyclic ancestor. Some species of these pseudo-monocyclic genera 

 have the primibrachs united by interbrachial plates. Schlueter 

 (4) has referred to Guettardicrinus, in which the primibrachs are 



