100 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



crinoids were in detached masses, clinging together and floating in the 

 open sea, entirely separate from other objects. They were actually 

 swarming, very much like a swarm of bees when they leave the liive 

 and settle upon some object — some on the outside and some buried 

 underneath their fellows — all in the utmost confusion. 



A. H. Clark (1909a, p. 129) devotes some attention to the ecology 

 of Uintacrinus, although he suggests notliing essentially new. In 

 one paragraph he arraigns authors as not having the " courage of their 

 convictions" in considering Uintacrinus as a pelagic type, as shown 

 by their figuring specimens with the mouth up. I think it has been 

 generally conceded that Uintacrinus floated with the arms dependent. 

 Indeed this is so obvious that no one has taken the trouble to point 

 it out hitherto. The figuring of Uintacrinus mouth up is not such an 

 evidence of weak faith as it seems to Clark, after all. This is the 

 conventional manner of illustrating crinoids, and is followed out 

 even in the case of the Calceocrinidge by Bather (1893). A plate 

 of Uintacrinus figures with the apical portions up would have to 

 be reversed by the average mortal before becoming intelUgible. 

 Clark likewise gives some interesting views relative to the feeding 

 habits of Uintacrinus. He considers that — 



the closer the individuals lived, the more advantageous it would be for them; for 

 their food probably consisted of minute pelagic organisms which they intercepted 

 with their long feathery arms; these organisms are largely lucifugous, and would 

 tend to collect under the shadow of a mass of crinoids as they are known to do under 

 floating logs and driftwood which, thereby, would be placed in the economically 

 advantageous attitude of attracting to itself without effort its own food supply. The 

 perisome of Uintacrinus is black, of such a dense carbonaceous black that it has been 

 preserved without change through the ages which have elapsed since cretaceous times; 

 and, if one of these small lucifugous organisms took refuge under the shadow of a 

 mass of Uintacrinus, it would be quite likely to be attracted to the blackest portion 

 of the animals, the disk or ambulacra, whereupon it would soon find its way (or 

 rather be conducted) to the mouth. 



Just why the disk is held to be black in the case of the living crinoids 

 it is difficult to say. As described by Springer (1901) the tegmen is 

 black, as carbonized animal tissues are apt to be. It has not hitherto 

 been held as remarkable that carbonized matter should retain its 

 blackness. Furthermore, the advantage of having the food attracted 

 to the disk is not immediately obvious. The hundreds of pinnules 

 borne on the arms are supposed to fimction as food-gathering organs, 

 and they would not be specially benefited by a black spot an inch 

 or so in diameter, several feet away. 



It is inconceivable that the animals could have hved under such 

 crowded conditions as has been predicated by the authors just quoted. 

 For what purpose were the extremely long arms and other very 

 special modifications other than that the animal might have the 

 utmost freedom of movement ? Again, how could any but a favored 

 few, and even those in but a very insufficient way, obtain nourishment ? 



