Crinoidea, Pentacrininae. 51 
raised, usually smooth, narrow, but merging insensibly into the radial ridge-groups. 
Petal-floors sharply depressed, smooth, or rarely granulate and that chiefly at their 
outer ends. usually lozenge-shaped, the short diameter of the lozenge bisecting the 
floor equally only in pentagonal ossicles, but approaching the lumen as the excav 
ation of the re-entrant angles increases; the lozenge may lose its lateral angles and 
so become lanceolate. The radial ridge-groups vary considerably in structure, but 
the variations form a connected series, though it may be doubted which end of 
the series is the more primitive. Thus, in some joint-faces they consist of adradial 
crenellae, similar to, and continous with, the peripheral crenellae, inosculating at an 
angle with those of the adjacent petal, i. e. arranged herring-bone fashion; in rare 
cases a few may meet gable-fashion; towards the lumen these crenellae become 
smaller and less regular, till they appear only as confused anastomosing granules; 
there has been found no specimen in which definite crenellae continue up to the 
central area. In the next stage a greater number of the crenellae have passed into 
the irregular granular condition, so that at last the whole ridge-group may be merely 
a raised granular area, with the granules increasing in size centrifugally. In what 
appears to be the next stage, the granules are arranged in two rows, continuing 
the lines of such crenellae as persist at the distal end. Finally the granules of each 
now fuse, so that the ridge-group now consists of two ridges that radiate from 
the central area and may either diverge or lie parallel. As variants on these main 
stages, the radial ridges are sometimes broken up into quite regular granules or 
small crenellae, which usually lie at right angles to the radius, and may meet 
across it, as in Balanocrinus; or they may even point towards the lumen, and, 
meeting thus, form reversed gables. The peripheral crenellae follow regularly on the 
normal adradial crenellae, the longest of all the crenellae being, as usual, those 
where the two series meet, their length varying inversely as the excavation of the 
re-entrant angle. The crenellae of each petal diverge from the interradius, sometimes 
fan-wise, but sometimes almost at the same angle so that those of each side are 
parallel. The number of peripheral crenellae in a petal varies from 6 or 7 in a 
columnal of 2°56 mm. diameter to 14 or 15 in columnars of 5 mm. to 7 mm. 
diameter. The number also increases, at the expense of the adradial crenellae, with 
the excavation of the re-entrant angles. The crenellae widen at their outer ends 
and usually run together, especially at the bottom of the intervening grooves, thus 
reducing the crenelation of the suture-line. 
A rebate edge may completely surround the joint-face, but broadens at the 
radii, forming radial triangles. The base of these is often excavate, and the apica 
angle always obtuse. The basal margin may be raised, especially on the radius, 
into a ridge or lip; and this may extend inwards as a radial crest. In one specimen 
the contrary variation has been observed, the radial region of the triangle being still 
more depressed. 
The following measurements in millimetres are from an internodal of average 
shape, size, and development : 
DIaIeten Ten vitlotp Reet) se (aes) 4) Bd 
WMensthrorunteradius aM iqsst! oly we at les ee Gee. 128 
Length of radius esis d te ka sy gOS» bs 22 
Distance from lumen to end of petal-floor. . . . . 2:2 
