106 SMITHSONIAN INSTITUTION 



porated, either by interbrachials alone (e. g., the form called Brahmacrinus by 

 Sollas, and certain species of Platycrinus) ; or by means of other brachials 

 which overlap the first and make it rigid (e. g., Marsipocrinus, Pterotocrinus, 

 etc.). Or, the modification may be towards a more flexible calyx as in the 

 Reteocrinidae, in which, however, the mouth and food-grooves are strictly sub- 

 tegminal. Such cases, in my opinion, must be treated as intermediate types, 

 transitions toward the Inadunata and Flexibilia respectively, which upon a 

 fair preponderance of the characters seem to go better within the Camerata 

 than anywhere else. Whether to leave them so, or to create independent divi- 

 sions for them, is a matter of expediency depending upon the individual point 

 of view. 



The Flexibilia are also specialized, and were similarly limited to the Paleo- 

 zoic, though there is a sporadic reappearance of some of their characters 

 among the Apiocrinidae and the comatulids. The Inadunate type, represent- 

 ing the most generalized structural plan of the crinoids — a calyx composed of 

 basals, radials and orals, which at some stage forms the entire calcareous 

 skeleton above the stem in every crinoid — is in its most essential features, 

 though variously modified, carried forward with the Articulata, and thus has 

 an unbroken range from the earliest Ordovician to the present time. These 

 three groups underwent more or less parallel modifications, with analogous 

 differentiation of characters for family divisions, some of which reappeared 

 independently in each of them. 



The Articulata, with their Neozoic range from Jurassic to Recent time, 

 present an aggregate of characters which seem to indicate a separate group, 

 broadly comparable to the other three but upon somewhat different criteria. 

 This method of treatment is a departure from the later plan of Wachsmuth 

 and Springer by way of a return to the earlier one, now reinforced, as it seems 

 to me, by more substantial reasons than before ; it has already been briefly sug- 

 gested by me in the new edition (1914) of the Zittel-Eastman Textbook of 

 Palaeontology. This view also accords with the conclusion reached by 

 Dr. Kirk as the result of independent researches on Certain Eleutherozoic 

 Pelmatozoa, 1 as follows: 



Among all the known post-Paleozoic Crinoidea there is an essential unity of structure 

 that points strongly to a not widely diverse origin. 



The chief characters relied upon to distinguish this order as extended and 

 denned by Miiller, viz.: (1) an open mouth and food-grooves, and (2) a sepa- 

 rate axial or dorsal canal perforating the arms, were clearly indecisive, con- 

 sidering that the first belongs equally to the entire Paleozoic group Flexibilia, 

 and the second is shared by a Devonian family and several genera of the 

 Inadunata. 



1 Proc. U. S. Nat. Mus., 41, 191 1, p. 81. 



