UINTACRINUS -. ITS STRUCTURE AND RELATIONS. 55 



way. Besides this, we have most conspicuously exhibited in Umiacrinus 

 the pliant test of the Flexihilia. 



Inadunata. Mr. Bather traces in Uintacrinus a direct morphological 

 resemblance to Dadocrinus, of this group. In the essentials of structure 

 upon which the great groups of Camerata, Inadunata, and Flexibilia have 

 been distinguished, Uintacrinus seems to me far more widely separated from 

 this group tlian from the others. It has an undoubted similarity in the 

 arms and pinnules, and in the arrangement of syzygies, to Dadocrinus. But 

 aside from these it possesses none of the characters which distinguish the 

 Inadunata. The absolute and deep incorporation of its brachials and fixed 

 pinnules into the calyx walls, is a character fundamentally inconsistent with 

 any position under the Inadunata. It is, of course, possible to imagine, as 

 suggested by him, that a gradual exaggeration of the features of Dado- 

 crinus, and loss of the stem, might have produced Uintacrinus, just as the 

 gradual addition of interbrachials to a Ci/cdhocrinus would produce a Cam- 

 erate Crinoid ; and this means nothing less than the transition, phyloge- 

 netically, from one primary group to another. It may be possible that 

 Dadocrinus, or some allied form, represents the line through which the 

 characters of Camerata, Flexibilia, and Inadunata came to be combined in 

 a convergent type such as this is. But if so, the line must include the 

 Comatulae, or at least the genus Actinometra, which has all the essential 

 characters of Uintacrinus except the interbrachials. 



MoNOcrcLiCA AXD DiCTCLiCA. Uintacrinus has both forms of base. If 

 these are tlie primordial characters by which all tlie Crinoids are to be 

 divided into two sub-classes, then the sole distinctive characters of each of 

 them are found converging in this Cretaceous species. 



It must be evident that the line of derivation of Uintacrinus will 

 have to be considered in connection with the Comatulte. Whatever its 

 ancestry may have been, it is quite plain that one of its near relatives 

 was Actinometra. The fossil Comatulte are said to range back to the 

 middle Lias, and arc fairly abundant in the Cretaceous. According to 

 Carpenter * Actinometra occurs in the Lower Oolites of both France and 

 England, and also in the Corallian of the Jura, and the Gault of the 

 English Cretaceous. 



* Chall. Rep. Comat., p. 37. 



