188 C. R. Keyes — Carboniferous Echinodermata 



Echinodermatous life during the Lower Carboniferous was 

 preeminently crinoidal and blastoidal : the former greatly pre- 

 dominating in the earlier part, and the latter conspicuously 

 present in the later portion of the period. So marked is the 

 contrast between the faunal features of the middle and upper 

 portions of the Lower Carboniferous that Wachsmuth and 

 Springer* have suggested that the Burlington and Keokuk 

 deposits could very appropriately be called the "crinoidal lime- 

 stone " ; while the St. Louis and Chester are manifestly a 

 " blastoidal " division. 



In the subjoined synopticalf table are arranged the principal 

 Carboniferous genera of the Pelmatozoa, and their distribution 

 through Paleozoic time. Inasmuch as the synonymy of the 

 species has been worked out more carefully and accurately than 

 in any other group of fossils, the table is especially reliable for 

 the consideration of problems of distribution during geologic 

 times. The figures in the various columns refer to the number 

 of species of each genus at present known from the respective 

 beds. In cases where species existed through more than one 

 epoch they are referred to the division in which they occur 

 most abundantly. The faunas of the Upper and Lower 

 Burlington limestones are so well marked that for convenience 

 the species of each are considered separately. The abbrevia- 

 tions are: L. S.= Lower Silurian, U. S. = Upper Silurian, D.= 

 Devonian, W. = Waverly or Kinderhook, L. B. = Lower Bur- 

 lington, U. B.= Upper Burlington, K.= Keokuk, L.=St. Louis, 

 C.= Chester, M.=Coal Measures. 



The genera enumerated in the accompanying synoptical 

 table, while characteristically Carboniferous, are very unequally 

 distributed in time. In nearly every instance each genus ex- 

 hibits : (1) a gradual expansion after its first appearance, 

 shown by the differentiation of species occurring in each 

 epoch ; (2) a culmination, marked not only by a larger num- 

 ber of species and a great numerical increase of individuals, 

 but also by a remarkable development and specialization of 

 various structural characters, and by a more or less wide distri- 

 bution in space ; and (3) a decrease in the number of species, 

 and a very apparent decline in physical energy, generally 

 terminating in a more or less abrupt extinction of the group. 

 The culmination of crinoidal:}: life generally was in the middle 



*Proc. Acad. Nat. Sci. Phila., 1878, p. 229. 



f The table is based chiefly upon the extensive collections of Messrs. Wachs- 

 muth and Springer. The echinoderms other than crinoids and blastoids have 

 purposely been omitted for the reason that at the present time perfect confusion 

 exists throughout. However, as accurately as can be determined from all avail- 

 able sources the omission affects in no way the general conclusions arrived at, in 

 regard to the Pelmatozoa alone. 



\ It must be borne in mind that the terms Crinoidea, Crinoids and their deriva- 

 tives are limited to ordinal application, equally with Blastoidea and Cystidea, 

 which are included under Pelmatozoa. There is a general practice prevalent of 

 applying the name Crinoidea to all stemmed echinoderms, thus making the term 

 co-extensive with Pelmatozoa, while in reality it is only a subdivision of the latter. 



