UINTACRmUS: ITS STEUCTUEE AND EELATIONS. 59 



the calyx, or fused with the infrabasals ; e. g., the IchthyocrinidoB.* This 

 results from the fact that generally in this group, so far as known, the 

 stem did not increase by the introduction of new columnals at the extreme 

 proximal end, but by their introduction next below it,t — the top columnal 

 remaining as a persistent proximale. Hence the stem would be most easily 

 detached at that point, and the top columnal would remain. 



A similar result is produced, either by atrophy or absorption of the stem, 

 or by its breaking off just below the proximale, in Millericriniis Pratti. % 

 May not Uintacrmiis, with its centrale a probable relic of the stem, repre- 

 sent that stage phylogenetically in which the stem has been permanently 

 lost at that point, as is actually the case with Adinometra and the other 

 Comatulae ? It seems to me that the few cases in which a free-floating 

 habit was developed among the Inadunata — such as AgassizocrinnSy in 

 which the whole stem disappears, and the top columnal does not remain to 

 form a centrodorsal or centrale — are by no means so suggestive of deriva- 

 tion as the facts just mentioned. Mr. Bather, in his new classification in 

 the Lankester Zoology, Pt. III., Chap. XI., p. 182, places Dadocrinus among 

 the Inadunata, and in the flimily Pentacrinidae. This family, so far as 

 known, has a central mouth, and a calcified ambulacral skeleton. Then he 

 places Actinometra among the Flexibilia. If this be correct, then a fortiori 

 why should not Uintacrinus, with its excentric mouth and open ambulacra, 

 in addition to its pliant test, separate axial canal, extensively developed 

 interbrachial system, and unstable base, go likewise with the Flexibilia, and 

 not with the Inadunata ? 



Of course it is possible, as Bather suggests, that the Pinnata were 

 derived from the Mesozoic Inadunata, and not from the Impinnata. The 

 pinnulate feature of the Puinata seems to be the chief reason for this sug- 

 gestion. It seems to me that if the possession of pinnules would not 

 remove a genus from the Cyathocrinoidea division of the Inadunata § there 

 is no controlling reason for supposing that a pinnulate may not be derived 

 from a pinnuleless form in course of geological time. The Impinnata have 

 about as ancient a lineage as the Inadunata, for they go back to the Lower 

 Silurian. It is also known now that they come down at least to the Coal 



* Wachsmuth and Springer, Mon. Crin. Cam., PI. II., Fig. 4 bj PI. VI., Pig. II. 

 t Ibid., pp. 39, 40, 152. 



X p. H. Carpenter. On Some New or Little Known Jurassic Crinoids. Quart. Jour. Geol. Soc., Feb. 

 1882, pp. 29-38, PI. I. 



§ Lankester Zoology, Pt. III., Ch. XL, p. 172. 



