38 UINTACRINUS : ITS STRUCTURE AXD RELATIONS. 



It may be that " Monocyclica Camerata" represents a nearer approach to 

 the flxct of nature tlian " Camerata Monocyclica," or simply " Camerata " ; 

 but 1 am not yet convinced of it. Whether evolution of the Crinoids was 

 in all cases along the line of basal, or of tegminal, development, we cannot 

 tell. If we are to be guided alone by the embryology oP Antedon, we should 

 be inclined to say it was the former. But I am by no means sure, as 

 has been suggested by both Neumayr and Carpenter, that we are justi- 

 fied in judging the phylogeny of the entire class by what we know of the 

 ontogeny of a single genus, which cannot be said to be, in all respects, a 

 typical one. 



The two forms run together so closely in the Lower Silurian that Wach?- 

 muth and Springer were unable to separate them more than generically. 

 And in many Mesozoic and recent Crinoids the dicyclic character is so com- 

 pletely lost in the adult that they were classed as monocyclic by everybody 

 until our discovery of the law of alternation made it possible to recognize 

 the dicyclic plan where the infrabasals are either concealed by the stem, or 

 totally obliterated by growth. Even then our statement that the Comatulae 

 are built on the dicyclic plan was unmercifully criticised and ridiculed by 

 P. H. Carpenter, until Bury's discovery of the infrabasals in the larva of 

 Antedon settled the question. 



At all events, we have in Uintacrinus perfect proof that in some cases 

 the characters of a monocyclic or dicyclic base are subordinate to others, 

 and do not mark the line of descent. 



STRUCTURE OF THE TEGMEN. 



An entirely new fact, which must be taken into account in discussing 

 the relations of Uintacrinus, must now be considered, and that is the 

 morphology of the ventral disk or tegmen, which is now for the first time 

 brought to light. Hill, in describing the fine material acquired by the 

 Kansas University in 1894, expressed the opinion that " from the shape 

 of the Crinoid, its globose form, and long, heavy arms, one would 

 hardly expect to find any of the ventral plates exposed, and such 

 is the case.  Nor has it been possible to expose ^ them by dissecting 



