THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Or 
Oo 
Carpenter * further states that in Pentaerinus Wyville-thomsoni the nodal 
joint from which the separation takes place “sometimes loses its ordinary 
characters altogether, becoming much enlarged and rounded below so as to be 
almost hemispherical in appearance.” And in a foot-note he says: “The un- 
usual enlargement of the nodal joint suggests the idea that the structures 
which have been described by Hall under the name Ancyroerinus + may be the 
detached stems of a Palzxocrinoid in the semi-free condition,” —in which we 
fully agree with him. Aneyroerinus has the form of an anchor, with four hook- 
like processes around a central ascending stem, which at its distal end is 
provided with a small, rounded tubercle, closing the opening of the central 
canal exactly as in some cases of Pentacrinus. That this stem is morphologi- 
eally in the same condition as that of Pentacrinus, nobody will deny after 
examining the specimens. The four lateral extensions were doubtless radi- 
cular cirri, whose joints were obliterated by calcareous overgrowth, as in the 
lower part of its tetramerous stem. 
Something similar to this may have taken place in other Paleozoic Cri- 
noids; and it is quite probable that the terminal end, as it appears in the 
specimens, is in many cases not homologous with the part by which the 
young Crinoid had been formerly attached, but is a product of later growth. 
We suspect this to be the case in the Actinocrinide, Platycrinidx, and other 
forms in which the terminal part tapers rapidly to a point, and cirri are 
given off from the sides. It would not be a great departure from the 
structure of the Comatule, if we bear in mind that their centro-dorsal is 
a modified stem joint, bearing cirri upon its outer surface. The only 
essential difference would be that in the Palzxocrinoid the stem separated 
at its Jower end, and in the Comatule at the upper. 
That the young Paleocrinoid in its early life was attached by a dorso- 
central, we may fairly infer from what we know of the development of the 
Comatule, and from paleontological evidence. The indications, however, 
leave it somewhat doubtful if the fixation was permanent. We believe that 
in the majority of cases among the older Crinoids the stem was afterwards 
separated from the root, and that the animal subsequently led a free 
life. In only two instances do we know that Paleozoic Crinoids were 
attached by what appears to have been originally a dorso-central plate: in 
* Challenger Rep. on the Stalked Crinoids, p. 19, and foot-note. 
+ Fifteenth Ann. Rep., N. Y. State Cab. Nat. Hist., 1862, pp. 89, 90. 
