SYSTEMATIC PART. 169 
throw new light upon important questions, and require the undoing of 
much previous work ;— as was illustrated in the case of the disk of the 
Ichthyocrinide, and by de Loriol’s discovery of small infrabasals in two 
species of Dillericrinus, which made important changes in the classification 
imperative. 
DEFINITION OF THE CRINOIDEA AND THEIR PRIMARY DIVISIONS. 
Class CRINOIDEA. 
Echinoderms which during part or all of their life were attached to other 
objects, either by means of a stem or directly by the abactinal side of the 
calyx. The visceral mass enclosed by a limestone test or calyx, constructed 
of plates symmetrically arranged, and giving off well defined, free arms 
from the sides. Mouth directed upwards. 
lie 
Crinoids in which the arms are free above the radials. The top 
joint the youngest in thestem . . . - - + + + +s = Order INADUNATA. 
A. Disk composed of orals only. Ambulacra subtegminal Suborder Larviformia. 
B. Posterior side of the disk extended into a sac. Am- 
bulacra supra-tegminal . . . - + + ee es Suborder Fistulata. 
Il. 
Crinoids in which the lower brachials take part in the dorsal cup. 
All plates of the calyx united by close suture. Mouth and 
food-grooves closed. The top joint the youngest in the stem. Order CAMERATA. 
II. 
Crinoids in which the lower brachials are incorporated into the 
ealyx either by lateral union with each other, or by supple- 
mentary plates, or a caleareous skin, All plates from the 
radials up movable. Mouth and food-grooves exposed. ithe 
top stem joint fused with the infrabasals, and not the youngest 
Fombtoe the Stems. i = 3 eis Pee ees Order ARTICULATA. 
A. Armsnon-pinnulate . . . .- . + + +++: > Suborder Impinnata. 
B. Arms pinnylate: - - -. - +. s+ 5 + © a © ® Suborder Pinnata. 
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