NO. 1846. ON CERTAIN ELEUTHEROZOIG PELMATOZOA—KIRK. 99 



exocylic tlisks that this close alUance with Actinometra is predicated. 

 These features as elsewhere noted I believe to be purely secondary 

 and induced by an eleutherozoic mode of life. Actinometra and 

 Vintacrinus I do not believe we may safely hold to be more closely 

 related than as having descended from a common 'p^e-Dadocrinus 

 ancestor. 



A. H.Clark (1909 h.) in placing TJintacrinus sj^stematically, groups 

 the Uintacrinidre and ]\Iarsupitid£e together under the ''Comatulida 

 Innatantes." His definition follows: 



Comatulida Innatantes: Pelagic comatulids in which the basals are not metamor- 

 phosed but form an integral part of the body wall; the infrabasals are not united with 

 the central plate, but usually form part of the body wall; occasionally, through indi- 

 vidual variation, they are absent; there is no evidence of attachment at any stage, 

 so that their central apical plate may possibly represent the dorso-central instead of 

 the centro-dorsal of other comatulids. The plates of the calyx, which is very large and 

 more or less globular, are very thin. 



Included families: I^Iarsupitidae; Uintacrinidse. 



This treatment is but slightly better than the time-honored and 

 discarded custom of placing the two genera into one family. It is to 

 be noted that he follows Springer in placing Vintacrinus wdtli the 

 Cbmatulae. Springer, however, while placing TJintacrinus among 

 the Comatulse, and consequently in his opinion, in the Flexibilia, 

 retains Marsuyites as a well-defined Inadunate. 



Ecology of Uintacrinus. — There can be little doubt but that UintOr 

 crinus was a pelagic type. Its extreme modifications to adapt it for 

 such an existence, and above all its lack of prehensile cirri or other 

 organs by means of which it could attach itself to extraneous objects, 

 coupled with the extreme length and flexibility of its arms, are 

 almost conclusive proof that such is the case. Such forms as 

 Agassizocrinus and the free Edriocrinus which likewise lacked cirri, 

 but which were decidedly not fitted for a pelagic existence, probably 

 rested on the bottom on their comparatively short arms. Indeed, it 

 is probable, as is shown elsewhere, that these forms crawled about a 

 good share of the time, rather than swam about freely. 



It is a debatable question whether Uintacrinus was as gregarious 

 in its habits as has generally been conceded hitherto. At the present 

 day, it is true, Antedon swims about in schools, and Actinometra 

 seems to be equally gregarious so far as observations have been made. 

 In the past, Agassizocrinus seems to have lived together in great 

 numbers, and the same was true of Saccocoma. These forms, how- 

 ever, I do not consider essentially pelagic as I do Marswpites and 

 TJintacrinus. In European deposits TJintacrinus has been found as 

 isolated specimens only. It is when we come to the Niobrara of 

 Kansas that we have to deal with the curious ''colonies" of TJinta- 

 crinus. Springer believes, as do all other writers on the subject, that 

 TJintacrinus was gregarious in habit. He says on page 11, ''These 



