HISTOEICAL. 25 



In 1879, a month or two after the appearance of von Zittel's Handbuch, 

 we published Part I. of our Kevision of the Palasocrinoideaj embracing the 

 Ichthyocrinidae and Cyathocrinidae ; and in 1881 Part IL, containing the 

 SphaBroidocrinidaB. In both parts we gave a review of the genera then 

 known, which were redescribed and systematically arranged. We also gave 

 with each genus a list of the species and their synonyms so far as then 

 known. No effort was made by us to subdivide the three groups, because, 

 as we thought, the knowledge of fossil Crinoids had not been advanced 

 sufficiently to justify it. We waited for the publication of the Challenger 

 Report, which we hoped would solve certain important morphological 

 questions. It seemed to us that a revision of the genera, many of which 

 had been incorrectly, others insufficiently, defined, and the arranging of 

 them systematically among a few large natural groups, was preferable to 

 a classification based upon unreliable data. We separated the Crinoids into 

 Palaeocrinoidea and Stomatocrinoidea,^ the latter to include all Mesozoic 

 and later forms. 



The name "Pal^ocrinoidea" had been introduced by Wachsmuth in 

 1877 as a subdivision of the Crinoidea^t to include those forms in which the 

 disk is roofed by a second integument, which he supposed to exist in all 

 Palaeozoic Crinoids. He recognized among the Palaeocrinoidea three dif- 

 ferent plans : — 



A. The Admocri7iiis plan : Tegmen rigid ; composed of heavy, rather 

 large, immovable plates, forming a free arch. 



B. The Taxocrinus plan : Tegmen flexible, consisting of minute, movable, 

 plates. 



C. The Cyathocrinus plan : Tegmen at the four regular sides composed 

 of a large interradial plate, the posterior side extended into a tube or sac ; 

 mouth and food grooves covered by small plates. 



The differentiations in the tegmen he thought w^ere accompanied by im- 

 portant modifications in the composition of the dorsal cup, and he expressed 

 the opinion that the construction of the tegmen afforded excellent charac- 

 ters for subdivisions. These divisions were actually made by us in the 

 Revision, Part III., and they form practically the foundation of our present 

 classification, notwithstanding that our views respecting the tegmen itself 

 have since then undergone considerable changes. 



* In place of Stomatocrlnoidea we afterwards adopted Carpenter's preferable name " Neocrinoidea." 

 f His paper " On the Construction of the Summit and its Value in Classification." — Amer. Jour. Sci. 

 and Arts (3d series), Vol. XIV., September, 1877. 



4 



