104 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



In these forms the centrale may be instead of centro-dorsal really the 

 dorso-central, in which case we should get an interesting homology 

 with the echinoids." 



Which paper has the precedence it is hard to say. It is quite evi- 

 dent, however, that in two papers, perhaps in press at the same 

 moment, he reverses himself without in either case referring to the 

 other paper.^ 



It is somewhat mystifying when and how Clark "independently 

 showed" that Uintacrinus had never been attached. That TJinta- 

 crinus has no column, so far as known, has been estabhshed by the 

 researches of Bather and Springer. The only way for Clark to prove 

 the absence of a column, or its presence for that matter, is to trace 

 the development of the form back until a stem is found, or back so 

 far in the ontogeny of the animal that there is no chance of a column 

 having been present. We shall await this proof with considerable 

 interest. 



The other two genera referable to Type II are of considerable inter- 

 est, but they are so well known that any extended discussion of their 

 structural features is scarcely warranted. There are, however, cer- 

 tain interesting structural deviations from those to be noted in the 

 case of Uintacrinus. These deviations form an interesting example 

 of adaptation to the same type of existence by crinoids belonging to 

 fairly unrelated genetic lines. Any conclusions to which we may 

 come relative to the derivation of these two genera are even more 

 nebulous than in the case of Uintacrinus. 



Marsupites. — In its adaptation to a free-swimming existence Mar- 

 swpites (PI. 10, fig. 4) differs from Uintacrinus in many important 

 regards. The arms are comparatively short and bifurcate many 

 times. The dorsal cup is large, but its size is due simply to the great 

 size of the three circlets of plates and of the centrale. There are no 

 interbrachials, and there is no incorporation of the proximal pinnules 

 in the cup. The tegmen is composed of rather heavy plates, 

 indicating the comparatively recent acquisition of a free-swimming 

 existence. 



In regard to this form Bell (1891, p. 210, footnote) has written: 

 "I suppose no morphologist will be bold enough to say whether 

 Marsupites or the irregular Blastoids are primarily or secondarily 

 free forms." This seems to be the stand taken by A. H. Clark, at 

 least in regard to Marsupites, as elsewhere quoted. It seems to me, 

 rather, that it would be a bold morphologist indeed who has the courage 

 to claim a primaiy free condition for these forms. Freedom is too 

 easily secured, and symmetry is far too difficult to acquire to warrant 

 such statements. 



1 Since writing the above I have been informed by Mr. Clark verbally that he believes Uintacrinus never 

 to have been attached by a column. 



