4.00 Dr. F. A. Bather on British Fossil Crinoids : 
shown. The petal-floors are shaped as in B. didactylus, are 
flat, and not so much depressed. The pentagonal lumen, 
with radial angles, has a diameter of about *2 mm. 
In such a joint-face the essential feature that gives the 
Balanocrinus character is the distinction between the peri- 
pheral crenellae and those of the ridge-groups as marked by 
the sudden change of length and of angle. Thus the angle 
made by the most adradial of the peripheral crenellae with 
the one next it isabout 32°, but that made with the adjacent 
crenella of the ridge-group is about 55°. There is actually 
more distinction in this way than was noted in B. didactylus. 
The actual number of peripheral crenellae is less than in 
B. didactylus, and, since in each case we are dealing with 
full-grown examples, this is not due to the size of the 
columnal. The length of those crenellae relative to the 
diameter of the columnal is less than in B. didactylus, and 
the transition from the interradial length to the adradial is 
more gradual; the shortness is rather a Balanocrinus cha- 
racter, but the gradual transition is as in [socrinus. 
As representing the Isocrinus type of normal joint-face 
may be taken one of the well-preserved fragments E 426 a 
(Fig. 6). This is subcircular, tending to pentagonal with 
rounded angles. Mean diameter 4°11 mm. Peripheral 
crenellae not more than 7, and less if the adradial ones be 
reckoned with the ridge-groups, into which they merge 
insensibly; length gradually passing from *5 mm. inter- 
radially to ‘7 mm. adradially ; evenly spaced, confluent 
externally, sometimes subconfluent internally. Ridge- 
groups: outer adradial crenellae only 3 or 4 in all, gabled 
alternating, with no sudden change of angle or size from 
the peripheral crenellae ; at 1:0 mm. or less from the peri- 
phery they change into the parallel radia] ridges, which are 
relatively wide (°8 mm.) and meet in a rather large central 
area only slightly less raised than themselves. The radial 
canal is rarely seen, for these specimens have no radial 
depression or pore apparent. Lumen pentagonal, with a 
diameter *3 mm. or less. Petal-floors kite-shaped, outwardly 
depressed, but rising towards the central area; they are 
pitted by minute canals for the passage of the ligament 
fibrils, dispersed over the middle of the floor, but on each 
side forming a straight series, which continues on to the 
central area, where the two series end in a pair of slightly 
larger canals. In vertical section these canals can be traced 
following a straight course through the stereom, which has 
a marked vertically fascicular structure, slightly denser at 
half the height of the ossicle where it was first formed. 
