132 ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
the form of a small ring-like rosette. Finally, the button-shaped centrodorsal, 
which is now beset with numerous cirri, detaches itself from the stalk, and the 
creature becomes capable of independent motion. 
The ontogeny of Antedon reveals the fact that the basals, orals, and stem 
represent the most primitive skeletal structures, while the radials and brachials 
are formed at a subsequent period. Similar evidence is afforded by numerous 
fossil Crinoids, in which the basals and column are very strongly developed, 
while the radials are mostly of inferior size, and the arms either rudimentary 
or absent.! 
Habitat—Existing Crinoids live together in large numbers, and inhabit 
depths ranging from shallow water to a maximum of about 3000 fathoms. 
Their distribution, however, is mostly very local. Fossil Crinoids also appear 
to have been gregarious in habit, and their remains are frequently found com- 
mingled with those of reef-building corals in Palaeozoic strata. Owing to the 
extremely delicate constitution of many of the skeletal parts, and the looseness 
with which the plates and segments are united, the Crinoid organism is by no 
means favourably adapted for preservation in the fossil state. Perfect crowns 
are of comparatively rare occurrence ; but, on the other hand, detached joints 
of the stem and arms are often very abundant, and occasionally form beds of 
considerable thickness. Crinoidal limestones-of greater or lesser extent are 
met with in numerous formations from the Ordovician to the Jura ; those of the 
Carboniferous and Muschelkalk (Trochitenkalk) being especially characteristic. 
Classification.—The first attempt to construct a classification of the Crinoids 
was that of J. S. Miller in 1821. Four groups differimg in the form and mode 
of union of the calyx plates were distinguished by Miller, as follows :—C. arti- 
culata, semiarticulata, inarticulata, and coadunata. The classification of Johannes 
Miiller, in 1841, was based upon a number of differential characters, such as 
the articular or close suture of the radials, the thickness of the calyx plates, the 
mobility of the arms, and the plated or coriaceous character of the ventral disk. 
Two principal groups were recognised: Articulata and Tesselata ; while a third 
(Costata) was constructed for the reception of the unique genus Saccocoma. 
T. and T. Austin and F. Roemer adopted the untenable divisions of Stalked 
and Unstalked Crinoids. 
The importance of Wachsmuth and Springer’s investigations on the structure 
of the calyx, especially of the tegmen, and on the orientation of the stem and 
its canals in monocyclic and dicyclic forms, cannot be overestimated. Two 
groups were put forward in their classification of 1879: Palacocrinoidea and 
Stomatocrinoidea (= Neocrinoidea, Carpenter) ; groups which correspond in the 
main with the Jesselata and Articulata of Johannes Miiller. This classification 
was subsequently abandoned, and a new one proposed for it in 1888, in 
which four principal orders were recognised, as follows: Camerata, Inadunata, 
Articulata, and Canaliculata ; the latter being nearly identical with the 
Articulata of Miiller. The Inadunata are further divided into the two sub- 
orders—lI. larviformia and I. fistulata ; but it is preferable to regard these groups 
1 [Some of the Ichthyocrinidae are almost identical, in fact, with the pedunculate stages of 
Antedon. Wachsmuth and Springer, from their observations on the orientation of the stem and its 
canal in fossil monocyclic and dicyclic Crinoids, were led to infer the presence of infrabasals in the 
nepionic or adult stages of many forms previously supposed to be without them. This. prediction 
was abundantly confirmed by Mr. Bury’s discovery of minute infrabasals in the gastrula larva of 
Antedon. See especially 7. Bury, Early Stages in the Development of Antedon rosaceus, Philos. 
Trans. vol. CLXXIX. pp. 257-301, 1889.—Trans. ] 
