234 Mr. F. A. Bather on British Fossil Crinoids : 
the arms, but apparently does not extend to their full length. 
Arms uniserial, very long, tapering little, bifurcating at 
lengthening intervals toward the upper parts into very nume- 
rous equal branches, the ultimate divisions being extremely 
attenuate.” u Arm-joints shorter than in Crotalocrinus , with 
parallel sutures ; those of adjacent branches opposite each 
other not alternating.” u Ambulacral furrows shallow, with 
covering-plates arranged in the usual way.” u Column 
round, very large, with short joints and thin walls ; canal 
round and of extremely large size.” 
It is not, of course, any one of these points of resemblance 
that is remarkable ; it is the total effect : the evidence, so to 
speak, is cumulative. But there are two points in the struc- 
ture of the Crotalocrinidse on which Wachsmuth and Springer 
have laid particular stress. 
The reticulate structure of the arms in Crotalocrinus 
depends on the combination of the following characters : — 
depth of ossicles dorso-ventrally, length of arms, extreme 
bifurcation at regular intervals, and lateral processes of ossicles. 
In all these points the arms of Enallocrinus resemble those of 
Crotalocrinus except that the bifurcation does not take place 
at such regular intervals, and the arms are not laterally con- 
nected. A development in the direction of such connexion 
has, however, been demonstrated by Wachsmuth and 
Springer. u Toward the upper ends of the arm-joints there 
are more or less conspicuous transverse projections — one from 
each side of the joint — which are more prominent and elon- 
gate at the ventral side. They border the arm-furrow, and 
give to the arm, when viewed from the side, a pectinate 
appearance, which is more strongly marked toward the distal 
ends of the arms.” “We have observed these projections on 
the arms,” add Messrs Wachsmuth and Springer, u only in 
the English specimens. We give it as a generic character, 
as we think it likely the Swedish ones will show it also when 
sufficiently well preserved ; and because we consider it of 
some importance, as representing the projections on the arms 
of Crotalocrinus by which these were connected, and thus 
exhibiting a tendency toward the reticulate structure.” Now 
the arms of Thenarocrinus not only resemble those of Enallo- 
crinus , and to a less extent of Crotalocrinus , in depth, length, 
and bifurcation, but they show undoubted indications of 
nascent lateral processes. In their position on the arm, and 
on the ossicle, and indeed in everything but size, the antero- 
lateral ridges of Thenarocrinus resemble the processes of 
Enallocrinus . 
