DISCOVERY OF THE DISK OF ONYCHOCRINUS 501 



crinidae, has the Taxocrinus anal structure thoroughly developed. 

 Only its habitus of closely abutting arms differentiates it from Taxo- 

 crinus, and it must therefore be considered simply as a somewhat 

 abrupt transition form from the Taxocrinidae toward the Ichthyo- 

 crinidae, or vice versa. But it is most interesting to note that in cer- 

 tain forms referred to Lecanocrinus we can almost see the transition 

 actually going on, in the same horizon and locality. In L. macropetalus, 

 from the Niagara group at Lockport, N. Y., we have a most charac- 

 teristic example of the first family — a rounded, ovoid crown, with a 

 perfectly even surface, with rays and arms fiat dorsally and in close 

 contact throughout (Plate VI, Figs. 13, 14). It has a single very 

 large anal plate rising above the level of the radials, and curving to a 

 point between the rays, which abut upon it at either side and close 

 over it in an arch. This plate is without depressions of any kind, 

 and is perfectly flush with the general curvature of the crown. In 

 certain other species from the same locality and horizon, this plate 

 begins to be depressed at the sides from the upper end down, so as to 

 leave a ridgelike elevation in the middle, quite resembling the base of 

 our so-called anal tube, while the full dimensions of the plate are still 

 retained. In some specimens of these forms we can see this median 

 ridge continued by a second small rounded plate, of the same form 

 and size, the large anal having lost its pointed angle and become 

 truncate to support this new plate. Here we have the beginning of 

 our armlike anal series. If the process is pushed a little further, so 

 that the depressed lateral margins of the large anal plate become 

 replaced by perisome, we shall have a complete Taxocrinus anal side, 

 and our Lecanocrinus will have been transformed into a Gnorimo- 

 crinus. It is now very curious that the tendency is actually in this 

 direction as to those other characters on which the two families have 

 been separated; for along with these changes in the anal plate there 

 appear marked depressions between the rays and their divisions, 

 which become rounded, with strong tendency to divergence in the 

 upper portions, and to long and delicate arms. Hall's Lecanocrinus 

 ornatus,^ and Ringueberg's L. nitidus, L. incisus, and L. excavatus,' 

 are forms in which this interesting modification occurs. I have de- 



1 Paleontology of New York, Vol II, Plate 44, Figs. 2a-m. 



2 Bulletin, Buffalo Society of Natural History, Vol. V, Plate i, Figs. 5, 6, and 7. 



