THE SYSTEMATIC POSITION OF THE CRINOID GENITS 



MARSUPITES. 



By Austin Hob art Clark, 



Assistant Curator, Division of Marine Invertebrates, U. S. National Museum. 



Some time ago I suggested the division of the great group of free 

 living crinoids known as the comatulids into three suborders, as 

 follows : 



Innatantes: Families Marsupitidse and Uintacrinidae. 



Oligophreata : Families Comasteridae, Zygometridse, Himero- 

 metridse, Stephanometridae, Pontiometridae, Mariametridae, Colobo- 

 metridae, Thalassometridae, Calometridae, and Tropiometridae. 



Macrophreata : Families Antedonidae, Atelecrinidae, and Penta- 

 metrocrinidae. 



At that time I was concerned mainly with the recent forms, and 

 so I did not wish to go into detail in regard to the processes of deduc- 

 tion by which I had arrived at the conclusion that Marsupites is 

 closely allied to the comatulids, the predominant type in the recent 

 seas. 



I owe it to my colaborators, however, to define my position, and 

 to state the reasons for my conclusion, so that they may judge for 

 themselves whether I am right or wrong. 



As I understand it, Marsupites is a pelagic comatulid, derived from 

 the common comatulid stock and owing its aberrant calyx structure 

 solely to its pelagic mode of life ; the calyx is the most primitive type 

 of comatulid calyx, serving the original purpose of protecting the 

 viscera; what development there has been was exactly the opposite 

 of that seen in all other comatulids, and resulted in enlarging the 

 dorsalmost plates instead of reducing them, as has happened in all 

 other forms. The arms alone have developed along the lines followed 

 by the other comatulids; judging from the material which I have 

 been able to examine, the arms are not only exactly like those of the 

 recent comatulid or pentacrinite, but are comparable only to the 

 arms of the more specialized types, in the latter only to those in the 

 yenus Endoxocrinus. 



It is in the arms that we get the only direct clue to the systematic 

 position of Marsupites; but this clue is positive and unmistakable; 



Proceedings U. S. National Museum, Vol. 40— No. 1845. 



649 



