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crinoidz it appears that in most of the so-called monocyclic forms, the 
orientation of the stem, central canal, and cirri agrees with the dicyclic 
type, the infrabasals being succeeded by a radial stem, as in those 
crinoids in which these plates are present but too small to be visible 
on account of being completely covered by the upper stem joint. 
Upon the strength of these observations, partly, these authors suggested 
that such forms either had small infrabasals hidden beneath the top 
stem joint, or those pieces had been represented in the larva. Other 
observations led to the same conclusion. In Extracrinus and in two 
species of Millericrinus, the former belonging to the Pentacrinidz, the 
latter to the Apiocrinide, two of the principal families of the Pseudo- 
monocyclia, small infrabasals actually exist, and it appears very improb- 
able that those plates should be present in genera of the same family, 
and even among species of the same genus, and absent in others, 
_ especially when the space which in some of them is occupied by small 
infrabasals, is vacant in others, and interradially disposed instead of 
radially as it would be if the space represented the axial canal. On 
applying these observations to the Comatule it was found that the 
outer angles of the top stem joint in the Pentacrinoid larva of the 
Antedon, and the angles of the centrodorsal in the mature animal, did 
not come under the rules laid down for the Monocyclica, and this led 
to the conclusion that the Comatule also were built upon the dicyclic 
plan, and had infrabasals in early life. The predictions, which had been 
based exclusively upon paleontological evidence were afterwards veri- 
fied by the observations of Bury, who actually found infrabasals in the 
ciliated larvaof Antedon. ‘They consist of three unequal pieces, which 
in the Pentacrinoid stage are fused together with the top joint, so as 
to form with the latter one large plate with the five angles radial in 
position. A similar fusion evidently takes place among palzozoic 
Ichthyocrinidz, in which the infrabasals are also coalesced with the 
upper stem joint, as is shown by specimens in which the stem is 
detached from the crown. These individuals are in the same condition 
morphologically, as the two species of Millericrinus figured by de 
Loriol, in which the infrabasals coalesce with the stem contrary to the 
other species of that genus, and allied forms having the infrabasals 
more or less completely fused with the top joint. As this structure 
prevents the formation of new joints directly beneath the calyx, it is 
contended, from the analogy, that in all forms in which the infrabasals 
coalesce with the stem, the new stem plates are introduced at some 
