390 Dr. F. A. Bather on British Fossil Crinoids: 
crinus generally, the radial excavation is never great, 
although often exaggerated by the crushing to which these 
stems seem peculiarly liable. Thus in a rather small and 
slightly crushed pentapetalon (E 22028) IR is 2°7 mm., and 
r.1°9mm. But in a well-marked pentapetalon of 7°3 mm. 
diameter (E 21961) the measurements are IR 3°6 mm., 
r. 2°38 mm. 
Since IR here equals half the diameter, the depth of the 
radial excavation is‘8 mm., or less than one-ninth of the 
whole. The outline of the joint-face, however, is in some 
specimens more petaloid than the cross-section at the 
middle of the columnal, because the radial pore lies at the 
bottom of a depression, which, as viewed from the joint-face, 
produces the illusory effect of a radial triangle. Thus the 
number of peripheral crenellae is increased to 14 or more ; 
the length of the radial ridge-groups is correspondingly 
lessened, but they are still composed in part of adradial 
crenellae following on the peripheral crenellae, so that on 
the whole the peculiarly Balanocrinid effect is obscured. At 
the same time the petal-floors are necessarily narrower, and, 
owing to the change in the radial ridge-groups, cease to be 
bounded by concave curves ; they assume, therefore, a sub- 
lanceolate or kite-shaped or pyriform outline similar to that 
of the normal Jsocrinus petal. In such forms the crenellae 
near the interradius usually cease to be confluent, so that in 
this region the suture is crenelate. Yet even in these forms 
the fused portions of the radial ridge-groups manifest their 
Balanocrinid nature. 
The Syzygial Faces, both epizygal and hypozygal, depart 
from the normal in the greater development of the crenellae. 
In a specimen with mean diameter 9°4 mm. (E 22027 ; 
Fig. 2) the main peripheral crenellae of a sector are still 
about 14, but, instead of being confluent, they tend to 
increase in number towards the periphery, either by forking 
or by intercalation of narrower shorter crenellae, or in both 
ways. An intercalated crenella on the epizygal corresponds 
to a fork on the opposed hypozygal, and vice versa. In the 
specimen referred to, which is a rounded pentagon with 
slight tendency to lobation, the normal crenellae on the 
interradii are still short, about 0°6 mm.; but the crenellae 
become gradually longer as the radius is approached, so that 
some attain a length of 16mm. The inner ends of these 
long crenellae die away gradually into the floor, and in some 
cases two normal crenellae may join, so that from a single 
stem spring two main branches, each of which forks again, 
