XI. Balanocrinus. 391 
while between the forks is an intercalated crenella, making 
five denticles at the periphery. The change from these 
peripheral crenellae to those of the radial ridge-groups is 
rather rapid, but the outermost adradial crenellae show a 
similar disposition to increase by the same methods. Thus 
the crenellae of the ridge-groups, so long as they can be 
distinguished, display a slight alternation in size. Inaradius 
4-3 mm. long the crenellae can be distinguished for about 
2°6 mm. from the periphery, after which they coalesce into 
the parallel or bowed ridges. These last do not unite to 
form a ring round the central area. The floors are much 
less depressed than in normal joint-faces, and may even be 
flush in some specimens. In the Epizygal the radial ridge- 
groups Jeading to the cirrus-facets (of which there are two in 
E 22027) are gradually raised towards the periphery from 
the point where the crenellae cease to be distinguishable. 
In the Hypozygal (which in the same specimen shows the 
indent of only one cirrus-facet) the corresponding tract is 
depressed, and the radial canal opeus outwardly into a strong 
V-shaped notch (Fig. 4). 
A similar tendency to multiplication of crenellae on ‘the » 
syzygial joint-face is well shown in Jsocrinus hercuniae Bather 
(1909, ‘Trias. Echin. Bakony,’ pl. iv. figs. 108-110), a 
species which in some respects approaches Balanocrinus. 
We pass now to the other variations seen in the Biarritz 
stem-fragments. Most of these have been alluded to by one 
or another of the previous writers, and have occasionally 
given rise to doubts concerning the homogeneity of the 
species. 
The transverse section is rarely quite symmetrical, but, 
apart from the modification due to the cirri, the variation 
from symmetry is clearly due to Mechanical Crushing. 
This has in some cases flattened the specimens into bands : 
in E 21943 the diameters are 10 mm. and 4°4 mm. This 
effect is not without interest, as indicating a very weak 
internal stereom. A further result of the crushing is the 
formation of five longitudinal cracks, so that such a stem is 
at first reminiscent of those Palaeozoic stems that are split 
into pentameres. The cracks in the Biarritz specimens, how- 
ever, are not confined to’ the radii, where any division into 
natural pentameres would occur, but are also on the inter- 
radii, or in other words at the outer apices of the sectors 
(EK 22026, cf. d’Archiac’s fig. 16a). Both positions are 
taken by the cracks in E 22025, and the fracture on the 
interradii contrasts with the clean jointing on the radii. 
