72 



UINTACRINUS: ITS STRUCTURE AND RELATIONS. 



TABLE E. 



Variations iu size of braoliials and number of iuterbrachials among twenty-one specimens of 

 ' Forbesiocnnus " of various sizes. 



Although the conclusion above stated has been generally accepted by 

 other authors, a demonstration of it by direct evidence has not heretofore 

 been given. It is rare, in studying fo.ssils, that an opportunity is presented 

 for comparison of fixcts in a series of specimens of such extent and variety 

 as is found in tlie collection of Uintacriiius before me in this investigation. 

 With single specimens, or only a few of them, one cannot always be sure 

 that the characters presented truly represent the species or genus as it is 

 actually limited in nature. Indeed we may be totally misled in our esti- 

 mate of its real character by something that is a mere individual peculi- 

 arity, e. ff. PI. VI., Fig. 5, on which, standing alone, we would say without 

 question that the genus had an anal plate. This is especially true of 

 Crinoids of the higher developed types, like the Camerata or Flexibilia, 

 by reason of the complexity of their structure. 



With a large series of specimens, however, the liability to error of this 

 kind is much reduced, and by aggregating the facts thus presented it 

 becomes possible to ascertain the rules that prevail in the structure and 



