COMATILIA, A REMARKABLE NEW GENUS OF UN- 

 STALKED CRINOIDS. 



By Austin Hobart Clark, 



Collabnralor. Division of Marine Invertebrates. 



The elaborate definition of the genus Actinometra (the family 

 Comastericla> as now understood) given by Dr. P. H. Carpenter in 

 the Challenger Reports, and the various additional characters 

 noted by him in different places in the same work, would seem 

 to have established its status definitely, and to have demonstrated 

 conclusively that it formed a well-circumscribed unit, very sharply 

 contrasted with the aggregation of species called by Doctor Carpen- 

 ter Antedon; in other words, that the recent free crinoids without 

 basals and with ten or more arms fall naturally into two well-defined 

 structural types, separated from each other by more numerous and 

 more important characters than exist between the various specific 

 groups within the two tjq^es. At the beginning of my studies I had 

 become convinced from the available material that the division of 

 these forms into two sharply contrasted groups was very artificial, 

 and could not stand the test of modern systematic methods, in the 

 light of our greatly increased knowledge. I therefore j^roposed to 

 recognize, instead of the two genera '•'' Antedon " and ^'■Actinometra " 

 used by Carpenter, five great divisions (the families Comasteridse, 

 Zygometridse, Himerometridse, Tropiometridse, and Thalassometridse) 

 Avhich covered exactly the same ground, except that the number of 

 included species was nearly, if not quite, doubled. Each of these 

 families appeared to me to be separated from the others by characters 

 of just as great importance as the Comasteridse (the old Actinometra) 

 was from any one of them. 



My suspicions in regard to many of the characters relied upon to 

 differentiate ^^Actinometra " from ^^ Antedon " have recently been con- 

 firmed in a most conclusive manner. In examining some comatulids 

 taken by the U. S. Bureau of Fisheries steamer Albatross in deep 

 water between the Bahama Islands and Cape Fear, North Carolina, 

 I found a most peculiar form which, according to the structure of 

 its oral pinnules and brachials, belongs to the Comasteridae, but 



Proceedings U. S. National Museum, Vol. XXXVI— No. 1668. 



361 



