24 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
boscis with the opening at the upper end: Gasterocomide, Platycrinde, 
Carpocrinide, Briarocrinide, Dimerocrinide, Barrandeocrinide, Actinocrinide, 
Stelidiocrinide, Melocrinide, Polypeitide, Uintacrinide, Glyptocrinde and Rho- 
docrinide. 
E. Tegmen bottle-shaped, narrower at the top; composed of large, 
polygonal plates, regularly arranged. Arms not extended beyond the calyx, 
biserial ; placed between rib-like projections, or occupying closed compart- 
ments: Culyptocrinide. 
The Articulata were defined by Zittel as follows: Plates of the dorsal cup 
generally very heavy, the articular faces excavated or smooth. Base mono- 
cyclic, and formed of five pieces; exceptionally dicyclic. Tegmen, as a 
rule, composed of a skin-like perisome, rarely plated; mouth and food 
grooves exposed. The mouth central; anus excentric; orals present or 
absent. Plates of the dorsal cup perforated by axial canals, passing out 
from the dorsal organ, and continued along the solid parts of the arms to 
the ends of the pinnules. 
To the Articulata he refers the following families: the Enerinide, Eugenia- 
erinide, Holopide, Plicatocrinidee, Apiocrinide, Pentacrinide and Comatulide. 
Examining the characters upon which Zittel separated the Tessellata 
from the Articulata, it appears that not one of his distinctions holds good 
throughout the families of either group. The “Taxocrinide” and “ Ichthyo- 
crinide,”’ which he refers to the Tessellata, have a more flexible disk than 
either the Encrinidw or Apiocrinide, and even than many of the Penta- 
crinide ; and, besides, have an open mouth and open food grooves. The 
Poteriocrinidx have a flexible disk, and well defined muscular articulations 
between the radials and costals. The interbrachials of Guettardicrinus and 
Apiocrinus roissyanus are as heavy and rigid as those of any Actinocrinus, and 
the plates of the dorsal cup in Eupachycrinus and Erisocrinus are perforated 
by axial canals, a character which was supposed to occur only among the 
Articulata. Neither is it true that the Articulata are “rarely dicyclic” ; 
the reverse would be more nearly correct, for most of them had small infra- 
basals in early life, which gradually fused with the stem. No doubt Zittel’s 
groups marked A and E form excellent divisions, but B, C, and D comprise 
widely differing types, and some of their families include monocyclic and 
dicyclic forms. As a whole, Zittel’s classification marks a great advance 
over those of his predecessors, and he is the first writer who gave a good 
definition of the families, and who arranged them systematically. 
