Morphologien! üesults. 
249 
among those Dendrocrinoidea that have pinnulate arms, usually bifurcating into two 
definite rami. In Encrinus itself the arms are so specialised in this particular 
direction that the genus cannot serve as starting-point for the later genera of Den¬ 
drocrinoidea with their more extended and usually more branched arms. In these 
later genera moreover the patina is reduced in size, vvhile the thecal cavity is 
enlarged, or at least maintained, by the upward extension of the flexible tegmen 
in such a way as to incorporate the proximal brachials in the cup. Such genera 
therefore fall into the Grade Articulata. The earlier forms of this plan of structure 
are represented in the Trias by Dadocrinus and Holocrinus, and there is some 
evidence from columnals that both these genera occurred in Bakony. Their frag- 
mentary remains unfortunately throvv no light on the origin of those two genera, 
and I can only repeat my Suggestion (1900) that they were descended from Car- 
boniferous Dendrocrinoidea in an earlier stage of arm-specialisation than that reached 
by Encrinus. 
The columnals found in Bakony do, however, comprise some forms of interest 
to the Student of evolution. The tendency of Encrinus columnals to assume a 
quinquelobate pattem is well known, and such specimens are noted on pages 11, 
12, 15, and 16. This pattern, however, rarely is so far developed as to suggest 
that the ligament-fibres of the stem were grouped in five as they are in the Pen- 
tacrininae. Entrochus insignis is more advanced in this direction, but may not have 
belonged to a true Encrinus. 
The small columnals from the Cassian beds of Cserhät, introduced as Entrochus 
qumqueradiatus (p. 19), have a distinct pentamerous symmetry, but it is doubtful 
whether any of the markings can be described as petaloid areas. In Holocrinus 
(p. 21), though of earlier date, portions of the stem had certainly attained this 
stage, and the crenellae were grouped round the five narrow areas. 
The columnals provisionally described as « Pentacrinus venustus» elucidate the 
origin of the Pentacrinine stem from the Entrochus plan. One factor in the evo¬ 
lution appears to have been the development of stem-cirri. In the earlier crinoids 
cirri are generally confined to the root end of the stem, where they are somewhat 
irregulär. In some stems of Carboniferous age, cirri occur at higher levels; but 
they are not in verticils, are unaccompanied by any obvious modification of the 
columnar joint-faces, and have no definite Orientation. In these forms the stem- 
lumen is relatively wide, and the nerves that pass from it to the cirri are therefore 
not restricted in direction. As the stem and its lumen become narrower, the axial 
nerves of the stem have less freedom of movement, and the branches arising from 
them tend to be strictly radial or interradial in position according to the radial or 
interradial Orientation of the axial cords. Thus the cirri also become definitely 
oriented. This Orientation becomes still more precise as the cirri fall into verticils, a 
structure that arises with the gradual development of syzygies and of the functions 
that they connote. This restriction of the lateral nerves to definite meridians must 
obviously have its effect on the stroma of the stem, and must tend, at all events 
in the neighbourhood of the verticils, to throvv the ligament-fibres into groups 
between the nerve-meridians. In this « Pentacrinus venustus», then, we see the 
crenellae retaining their primitive length immediately above the cirri, but in the 
intervening spaces they are shortened; and we may infer that this shortening is 
due to the concentration of the ligament-bundles. This structure is still far removed 
