DISCOVERY OF THE DISK OF ONYCHOCRINUS 487 



In the second family group, as formerly defined, subsequent 

 observations have led me to make some important modifications of 

 the arrangement heretofore proposed by me. It has long seemed 

 desirable to find some basis for separating the Silurian species of 

 Taxocrinus from the Carboniferous. Considering the changes that 

 have taken place in other types of this group, and especially since 

 the discovery of the facts above stated as to the Ichthyocrini, it 

 seemed to me to the last degree improbable that such a form as 

 Taxocrinus should persist from the Lower Silurian to the latest Sub- 

 carboniferous, without any modification of more than specific impor- 

 tance. Yet upon the basis of any of the characters hitherto regarded 

 as important in this group I was unable to find satisfactory ground 

 for distinction. I was at first strongly disposed to believe that the 

 Gotland species must all, if correctly observed, prove to have an 

 unsymmetrical calyx — that is, with a radianal — and thus belong to 

 Gnorimocrinus . But a careful re-examination by Mr. Liljevall of 

 all the specimens at Stockholm, with detailed drawings of each, has 

 convinced me that Angelin's T. rigens and T. ohlongatus have no 

 trace of a radianal. The type specimens of T. elegans and T. laevis, 

 from the Lower Silurian of Canada, do not show the anal side, but 

 when discovered I should expect to find a radianal.'^ 



Finally, however, the solution presented itself in a very simple 

 matter, which has been overlooked hitherto in all researches upon 

 the classification of this group, but which, upon consideration, appears 

 to be of considerable importance. It lies in the condition of the rays 

 below the first bifurcation — that is, of the brachials of the first order. 

 On account of some irregularity in a few cases noted by early obser- 

 vers, it has been handed down as a tradition, and religiously observed, 

 almost since the time of Phillips, that such irregularity in the branch- 

 ing of the rays was a characteristic of the whole group. This fact 

 seems to have diverted attention from the real significance of this 

 structure. In the Revision of the' Palceocrinoidea this opinion was 

 expressed, and in proof of it allusion was made to the differences in 

 the rays of Ichthyocrinus, which are discussed herein, and shown to 



I Since the above was written, specimens of both species have been found show- 

 ing the posterior side, and each has a large radianal in primitive position under the 

 right posterior ray. 



