XI. Balanocrimis. 389 



perhaps in the newly-formed columnals of the proximal 

 region in older stages, the arrangement may depart less 

 from that of Isocrinus. This is shown in the following 

 figures of de Loriol's plates in ' Paleoutologie Fraufaise ' : 

 pi. clxxxiii. figs. 6 b, 7 b ; pi. clxxxvi. fig. 11 b ; and to a less 

 extent in otliers. On the other hand, columnals of Isocrinus 

 may sometimes approach the Balanocrinus plan. 



Description of B. didactylus. — Turning now to the specimens 

 from Biarritz, we note that the Normal Joint-face is of 

 markedly Balanocrinus type. There is some variation, but in 

 a fully-grown columnal of 9 mm. diameter, from a median 

 or distal region of approximately circular section (E 21948), 

 the arrangement is as follows (Fig. 1) : — 



Outline subcircular, being slightly flattened on the inter- 

 radii and cut into on the radii where the radial pore enters. 

 Peripheral crenellae in each sector about 10, at right angles 

 to the periphery, unequally spaced and of unequal thickness, 

 those nearer the radii being stouter and sometimes double, 

 length about 1 mm., but longer towards the radii (1*3 mm.) 

 and rather shorter on the interradius, sometimes slightly 

 curved or waved in their course, confluent externally, so that 

 the suture is not crenelate. Occasionally a slight marginal 

 rebate. Radial ridge-groups : about 3 outer pairs of adradial 

 crenellae, continuing the slope of the adjacent peripheral 

 crenellae, are gable-shaped, but rapidly decrease in size, and 

 are succeeded by a series of minute crenellae, which, when 

 visible, are in opposed pairs, but which generally unite 

 radially to form a couple of ridges leading to the central 

 area. These ridges are separated by the radial canal ; 

 towards the middle of their course they thicken and may be 

 wider apart, attaining a width over all of 1 mm. ; towards 

 the centre they taper and again draw together, generally 

 meeting with one another and with their neighbours, so as 

 to form a narrow ring round the lumen, which ring corre- 

 sponds to the central area. Lumen subpentagonal, diameter 

 0'4 mm. Floors depressed or even excavate, bounded 

 adradially by concave curves (due to the widening of the 

 radial ridge-groups). 



It follows without doubt from this description that the 

 species is rightly referred to Balanocrinus. 



Such variations as occur in the normal joint-face, other 

 than those already indicated, are correlated with the variation 

 in Transverse Section. This assumes all the forms possible 

 to a Peutacrinid stem, with this proviso — that, as in Balano- 



