54 UmTACRINUS : ITS STKUCTUEE AND RELATIONS. 



most highly developed Camerata ; and its first brachial occupies the entire 

 width of the radial. It differs from Marsupites as Slrotocrinus differs from 

 Cyathocrinus, and these differences are sufficient to refer them to different 

 sub-orders. . 



Among the many remarkable things about this strange form, none is 

 more striking than the extraordinary way in which Uintacrinus combines 

 several characters which belong to the great primary divisions of the 

 Crinoids : — 



Camerata. In the manner in which the proximal pinnules are fixed 

 by the growth of interbrachial plates, we have a repetition of the peculi- 

 arities of certain highly typical Camerate genera. In forms like Strotocrtms, 

 Teleiocriniis, etc., where the side arms, branching alternately from each suc- 

 cessive brachial, may be considered as modified pinnules, we find the lower 

 ones fixed and incorporated into the calyx* by sutural connection with 

 interbrachials, intersecundibrachs, and even intertertibrachs. This occurs 

 also in Melocrimis. t In Gli/ptocrinus and Reteocriniis, however, two of the 

 oldest genera, we have the lower pinnules themselves fixed in a similar 

 manner.^ If any one will compare the disposition of the plates in the 

 interbrachial system of Glyptocrmus Di/eri, and the mode of fixation of its 

 lower pinnules, with the corresponding parts in Uintacrinus^ he will be com- 

 pelled to admit that in this feature of their organization no two Crinoids 

 could be structurally more nearly alike than these. The large size of the 

 body cavity, resulting from the great development of the interbrachial 

 plates, is also a character in which it resembles the Camerata, and the 

 Flexibilia as well, and in this respect it shows a marked departure from 

 the Inadunata. 



Flexibilia (Articulata, sensu W. & Sp ). If we consider such genera as 

 Sagenocriniis, from the Silurian, and Taxocrinus from the Silurian to the Car- 

 boniferous, we will find that the interbrachial systems of these forms are 

 substantially the same as that of Uintacrinus, giving rise to a similar 

 enlargement of the visceral cavity. The fixed pinnules are wanting here, 

 because there are no pinnules in the Impinnata division of this group ; but 

 otherwise the interbrachial and intersecundibrach spaces are filled with sup- 

 plementary plates in the same way, so as to produce a greatly expanded, 

 rotund calyx ; and they also increase in number with growth in a similar 



* Mon. Crinoidea Camerata, PI. LXV., Figs, la, Ic, 2a. f Ibid., PI. XXIII. , Pig. 1. 



X Ibid., p. 84, PL XIX., Pig. 1 ; XX., Pig. 1. 



