270 PALAEONTOLOGY OF ILLINOIS. 



in all other known points of structure, and present so many gradations in this 

 character, that we doubt the propriety of making it alone a full generic distinc- 

 tion. It is true, by taking out of the series the species forming the Onychocrinus 

 group, which we are now inclined to admit as generically distinct, the gradation 

 from Taxocrinus to Forbesiocrinus is not so complete as we had supposed ; still, 

 when we remember that the typical species of Taxocrinus vary in the number 

 of these pieces from none to two or three to each space, and those of Forbesio- 

 crinus from seven or eight to thirty or forty, while in the latter group individ- 

 uals of the same species sometimes present a difference of as many as ten of 

 these pieces to each space, we are still inclined to regard this as merely a sub- 

 generic distinction. Possibly other characters may yet be found for the sepa- 

 ration of these groups generically; but until such other distinctions are known 

 to exist, we prefer to range them as sections of the same genus, as follows : 



1. TAXOCRINUS, Phillips (proper). 



Species without interradial or anal pieces, or with not more than one to three 



in each space. 

 Examples. — T. macrodactylus and T. Egertoni, Phillips; T. nuntius, T. communis, 



and T. Kellogi=(Forbesiocrinus hunlius, F. commuis, etc., Hall.) 



2. lOBBESlOtKlSUS, be Koninck and Leiion. 



Species with from seven or eight to thirty or more interradial and anal pieces to 



each space. 

 Examples. — F.nobilis, deKoninckand Lehon; F. Worthem and F. Agassizi, Hall. 



As first proposed by Phillips, the genus Taxocrinus included his Poteriocri- 

 nus? Egertoni, Cyathecrinus tubevculatus, Miller, and G.f macrodactylus and 

 C. ? nobilis, Phillips. The first of these, which is a Carboniferous species r and 

 agrees in all respects with this genus, as generally understood, shows, accord- 

 ing to Phillips's figure, no interradial pieces; and but a single anal piece. The 

 second species, which is from the Upper Silurian, and is also generally regarded 

 as a typical Taxocrinus, shows, according to Murchison's figure (Siluria, pi. 14, 

 figs. 5 and 6), a single interradial piece, resting between the short, superior 

 lateral, truncated side of each two of the first primary radials ; while Miller's 

 figure of the same, as reproduced by Pictet (we have not Miller's work at hand), 

 shows on the anal side, apparently two small anal plates, resting side by side 

 down on the short, superior truncated side of one of the subradials. The third 

 species, T. macrodactylus, Phillips, also shows, according to. his figure {pi. xv, 

 Palaeozoic Fossils), one interradial, while his T. %iobilis is figured so as to show 

 of these intermediate pieces, one in one space, and three or more in another, 

 and is even supposed by de Koninck and and Lehon to be possibly the same 

 species upon which they proposed to found the genus Forbesiocrinus. So that 

 it seems very probable that, as understood by Phillips, his genus Taxocrinus 

 may have included both types, though all the species included by him, with 



