28 
Trias sic Echinoderms of Bakony. 
a radial c a n a 1, running from the central area (not from the actual lumen) to the peri- 
phery, where it is visible on the suture-line as a radial pore («interarticular pore» 
P. H. Carpenter) ; this structure is generally limited to the proximal region of the stem. 
In most cölumnals of Isocrinus, especially those from the distal region of the stem, the 
radial space is either limited to a small triangle or obliterated, and the adradial crenellae 
of one petal meet those of the adjacent petal, either inosculating and alternating with them, 
or joining symmetrically at their ends to form a series of gables, of which the apex is 
acentral. Such combinations of adradial crenellae may conveniently be spoken of as pe r- 
radial crenellae, constituting radial ridge-grou ps. In Balanocrinus the per¬ 
radial crenellae are not gable-shaped but lie almost straight across the perradius, while in 
extreme cases they become so short that the radial ridge-groups are little more than single 
lines of granules. There is no morphological distinction between a peripheral and an adradial 
crenella. With the growth of the columnal, peripheral crenellae gradually become adradial, 
and eventually perradial, while new crenellae make their appearance at the interradius. 
Therefore in any columnal these last are the shortest of the peripheral crenellae, and the 
outermost or adradial peripheral crenellae are the longest of all. 
The outcrop of the crenellae on the periphery produces a crenelate suture-line. 
But peripheral crenellae may exist without the crenelation of the suture-line being obvious. 
This happens when there is a rebate rim to the joint-face, the two rebates producing by 
their apposition a depressed suture-line, as explained above. This rim appears to be a later 
formation, and therefore may not be found in all cölumnals of an individual. The external 
crenelation is still more obscured when the outer ends of the crenellae are confluent, 
so that the grooves between them are partly or wholly filled up; thus the suture-line becomes 
only faintly sinuous, or even straight. 
The syzygial joint-faces are modified from the normal in two ways: first, by the 
obscuration or even obliteration of the normal rosette; secondly by the development of 
special structures in its place. The former modification, which increases with age, affects 
both epizygal and hypozygal faces in a similar manner, but is generally more pronounced 
on the epizygal. The latter affects the two faces differently. Thus, both faces are usually 
more indented radially than are normal joint-faces, but the indentation is greater on the 
epizygal. The petals of the epizygal are usually hollowed, in which case those of the 
hypozygal are swollen, so as to fit into the hollows. The radial spaces of the epizygal are 
sometimes raised, forming as it were an arch over the cirrus-facet and its lumen ; in that 
case there is a corresponding depression in the hypozygal. Sometimes, while the crenellae 
homologous with those of the normal joints become almost or quite obliterated, a fresh sei 
of very much finer and shallower crenellae appears in their place (see, for example, Isocrinus 
Hercuniae, pl. IV, fig. 109). 
Each cirrus is articulated to the nodal by a cirrus-facet. Most species bear 5 of 
these on each nodal, and that number is to be understood unless the contrary is stated. 
Some species are altern i-cirrate (see P. H. Carpenter «Challenger Report, Stalked 
Crinoids» sub Pentacrinus alternicirrus), that is to say, bear two cirri on one node, 
three cirri on the next, and so on, always alternating in radial position. The cirrus-facet 
may be indented, flu sh, or raised. In outline it is usually elliptical, and, except 
in Pentacrinus (s. str.), the long axis is t r a n s v e r s e, i. e. parallel to the columnar 
joints ; such a transverse ellipse may become ellipsoidal by the flattening of the upper 
or lower margin. In Pentacrinus the long axis is vertical and the ellipse may become 
rhomboidal, o v o i d, or even p y r i f o r m. The facet has a lumen emerging on the 
