HISTORICAL. 25 
In 1879, a month or two after the appearance of von Zittel’s Handbuch, 
we published Part I. of our Revision of the Paleocrinoidea, embracing the 
Ichthyocrinide and Cyathocrinide ; and in 1881 Part II., containing the 
Spheroidocrinide. 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 
Paleeocrinoidea and Stomatocrinoidea,* the latter to include all Mesozoic 
and later forms. 
The name “Paleocrinoidea” 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 
Paleozoic Crinoids. He recognized among the Palocrinoidea three dif- 
ferent plans : — 
A. The Aetinocrinus plan: Tegmen rigid ; composed of heavy, rather 
large, immovable plates, forming a free arch, 
B. The Tuxocrinus 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 teemen he thought were 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, 
* Tn place of Stomatocrinoidea we afterwards adopted Carpenter’s preferable name “ Neocrinoidea.” 
+ 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 
