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Show 1895.] MR. F. A. BATHER ON UINTACRINUS. 999 arguments of those eminent authorities who, with Neumayr (6), " regard it as most probable that Uintacrinus is a last straggler of the Ichthyocrinidae," yet I cannot but consider the counterarguments, here first definitely stated, as of even greater weight. One may also add the fact that none of the known Plexibilia show that predilection for a free mode of life that is so common in the order next to be considered. Turning to the Inadunata, w e have to choose between monocyclic 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 Marsupites. 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 development of certain other radials. Prom these more symmetrical forms, again, must be removed those that have simple unbranched arms, such as Hoplocrinus, Hybocrinus, Symbathocrinus, and Cupresso-crinus. Iocrinus, with its dichotomus, non-pinnulate arms, is also out of the question; while one need hardly mention such undeveloped genera as Gasterocoma, Lageniocrinus, and Allagecrinus. Thus Belemnocrinus, if correctly placed here, is the only genus remaining; in its bifurcate, sub-pinnulate arms, 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 n o w narrowed down to the Inadunata dicyclica and their descendants in the Mesozoic era, the Canali-culata. The earlier fistulate forms, with their asymmetrical anal areas, m ay be at once set aside; so may all genera with many-branched arms, whether pinnulate or non-pinnulate. Thus w e are restricted to such genera as Erisocrinus, Stemmatocrinus, Encrinus, Dadocrinus, and some species of Pentacrinidse. At first sight there appears mighty little resemblance between these and Uintacrinus ; so little that no one has ever dreamed of mentioning them in this connection. Yet it is here, and here only, that w e 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-monocyclic 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 |