166 ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
present in nepionic, frequently also in the adult stages. Plates of the dorsal cup 
heavy ; basals and radials united by close suture ; radials and lower brachials by 
muscular articulation or by syzygy. Radials laterally in contact, except in. Thawmato- 
crinus ; but small irregular plates are frequently interposed between the costals and 
distichals. Anal plates represented only in the larval stages. Arms wniserial and 
pinnulate, the ossicles pierced by a dorsal canal. ‘Trias to Recent. 
The Articulata include all Recent, Tertiary, and Mesozoic Crinoids, with the 
exception of Mursupites, Uintacrinus [and Encrinus, according to Wachsmuth 
and Springer]. They are chiefly characterised by the exposed condition of 
the mouth and food-grooves, as well as by a canal which perforates the arms. 
This is known as the dorsal or axial canal, and 
contains a nerve-band and fibres of connective 
tissue. Starting from the dorsally situated 
chambered organ (Fig. 276), there are five canals 
which traverse the basals as far as the centre, 
where they divide into two branches which con- 
tinue upward through the radials and brachials ; 
and there is also in the radials a ring - canal 
which serves to connect the longitudinal canals 
with one another. In young individuals these 
canals are in the form of open grooves on the 
inner side of the plates, but they become per- 
Ae fectly closed in the adult condition. 
Diagram showing course of axial canals [To the <Articulata (Articulosa) Wachsmuth 
in the calyxandarms of Enerinus. Canals and Springer refer only the Pseuwdomonocyelica ; 
represented by dotted lines when pene- > a ° : 
trating the interior of the plates, and by that is to say, Crinoids which are constructed 
ae. Ce UCRTES REN mer on the dicyclic plan, but in which the infra- 
basals are rudimentary, and are more or less 
completely fused with the top stem-joint, and in which the last-named joint 
is not the youngest in the stem, as is the case in all other forms. The 
families thus embraced are the Apiocrinidac, Bourgueticrinidae, Eugeniacrinidae, 
and Comatulidae among Mesozoic and later Crinoids, and the Ichthyocrinidae 
among the Palaeozoic. The Ichthyocrinidae, which are devoid of pinnules, 
are placed in the sub-group Articulata Impinnata ; the others, which are all 
pinnulate, constitute the sub-order Articulata Pinnata. The Pentacrinidae and 
Encrinidae, both of which are in all probability derived from the Poteriocrinidae, 
are assigned by these authors to the Fistulata, and the same is also true of 
the Plicatocrinidae and Holopidae, in which the top stem-joint is the youngest 
joint of the column wherever the latter is represented. | 

Family 1. Encrinidae. Roemer. 
Dorsal cup low, saucer-shaped, with dicyclic base. Infrabasals five, very small, 
and covered by the upper stem-joint. Basals five, large ; radials five, the articular 
faces truncate, and provided with transverse ridges. Interbrachials absent, teymen tn 
the form of a vault. Arms 5 x 2 or 5x 4; heavy and simple, closely abutting, and 
either biserial or composed of alternately arranged cuneate joints. Column round, 
rarely giving off cirri; the terminal end thickened and laterally eatended. Trias. 
Ewcrinus, Miiller (Figs. 276-278). & succeeded by two costals, of which 
