488 FRANK SPRINGER 



be due to the presence of a radianal uniformly in one ray; and to 

 the case of Forbesiocrinus agassizi, which will be considered later. 

 I have often heard Wachsmuth emphasize the statement that not 

 only are there irregularities in the rays, but that such irregularity 

 was a positive character of the group. 



If we take a specimen like Taxocrinus affinis Mueller,' we see that 

 the ray bifurcates on the second plate above the radial; or, in other 

 words, the ray has two brachials of the first order, or primibrachs. 

 Examining then the figure of Taxocrinus splendens M. and G.,'' from 

 Crawfordsville, Ind. — the best known Carboniferous species, and found 

 under other names in collections the world over — we shall find that 

 the bifurcation of the ray occurs on the third plate above the radial; 

 that is, it has three brachials of the first order, or primibrachs. The 

 first of these plans is that which prevails throughout the Camerata, 

 with a few exceptions, some of which can usually be explained by 

 the anchylosis or syzygial union of two plates. It now proves to 

 be a fact that it is also the structure of almost every one of the Silurian 

 and most of the Devonian forms of the Flexibilia, with a very few 

 exceptional cases, some of which I believe may be traceable to abnor- 

 mal specimens. It follows feebly down into the Carboniferous in 

 the genera Synerocrinus, Wachsmuthicrinus, Mespilocrinus, and 

 Metichthyocrinus, all of which are rare fossils. It ceased in the Paleo- 

 zoic, so far as we know, with the Keokuk Limestone, nothing of that 

 form having been seen from the Warsaw, St. Louis, or Kaskaskia, 

 beyond a few individually exceptional cases. Afterwards it appears 

 to have resumed its sway in the group, for it prevails through the 

 Mesozoic and to the present time in the great genera of the Flexibilia 

 Pinnata- — Apiocrinus, Millericrinus, Uintacrinus, Antedon, and 

 Actinometra; the two primibrachs in the later two genera being 

 sometimes united by syzygy. 



The second plan, while it may be exceptionally indicated by a 

 few cases in the Silurian and Devonian, became the leading feature 

 of the Carboniferous Flexibilia, where it is conspicuous in numerous 

 species of the widely distributed genera Taxocrinus and Forbesio- 

 crinus, from the Waverly to the Kaskaskia; Parichthyocrinus in the 



1 Mon. Echinod. Eifler-Kalkes, Schultze, Plate 4, Fig. 2. 



2 Bulletin No. 8, State Museum of Illinois, Plate 5, Fig. 3. 



