Echinoid Radiales, Radiolus raiblianus. 
217 
since the fragments h and j come from the distal half of the shaft, and since their 
rate of tapering is very slow, it is clear that such an estimate of length is far too 
small; h might well have attained a length of 60 mm. 
The Ornament consists almost entirely of pustules, which are rounded, tending 
to thorn-like, with a slight distal rake, and are, even when most prominent, quite 
low in relation to the thickness of the shaft; e. g. in e they project 0'3 mm., in 
h, at most 0'4 mm., and this last is the largest to be found. According to the 
distribution of the pustules, the specimens may be divided into two sets, which 
I do not venture to call varieties. In specimens a, b, c, f, g, h, j, m, n, o, p, 
the distribution is either quite irregulär or in somewhat ill-defined longitudinal 
rows. The latter condition is best seen in b, c, and f. In these rows the pus¬ 
tules are far apart, from 1'7 to 2 8 mm., according to the size of the radiole, while 
the rows themselves are much closer, say one to a millimetre. Since the pustules 
alternate in Position in adjacent rows, they also become arranged in oblique series, 
sometimes Crossing as in b, sometimes only noticeable in one direction. In g and 
p this oblique seriation is clear, while the longitudinal series cannot be made out. 
This then forms a transition to the mode of distribution seen in specimens d, 
e, k, and q, where, at least on one of the faces, the pustules are in distinct 
transverse rows. In specimen e there are on one face seven such rows, those 
near the middle of the shaft being 3 mm apart. The pustules forming these trans¬ 
verse rows are also arranged in longitudinal rows, of which 6 can be traced from 
end to end, while in the proximal region there are two others. 
Besides pustules, other features are occasionally present in the Ornament, 
and may be studied in specimen e. Although the pustules are not raised on ridges, 
as in C. parastadifera for instance, still traces of ridges, formed apparently of 
coalesced pustules, are visible at the proximal end of the shaft on both faces, 
but continuing rather further on the face that does not bear the transverse rows. 
That face also shows fine pustules or coarse granules between the larger pustules. 
Other specimens show the proximal ridges, but none the granules. 
The base, as may be gathered from the table of measurements, has, at the 
annulus, a diameter about half the greatest diameter of the shaft. The average 
ratio of all the specimens is 055. 
The acetabulum is deep, usually circular; its margin prominent, rounded, 
smooth. From it the base slopes equably to the annulus, which is broad, rounded, 
smooth The collerette appears to be little more than a well-marked groove, rarely 
attaining a height of 0'6 mm., as in g, and occasionally with its distal border very 
slightly raised. It may be followed by a short, smooth handle to the shaft, a feature 
most pronounced in e, where it has a height of 17 mm., the collerette here being 
a mere line. The ridges and grooves of the base are usually at right angles to the 
main axis of the radiole, and show scarcely any trace of dorso-ventral compression. 
Measurements in millimetres: 
a 
b 
c 
d 
e 
/ 
h 
J 
1 .ength.. . 
157 
167 
14'+ 17'+ 237 
147+23'5+ 23'6 + 257+ 
Greatest diam. dorso-ventral 
3-4 
3’4 
3'5 
47 
4'4 
46 
5'2 
4'5 
6'6 
Greatest diameter transverse 
3'7 
3'6 
3-9 
4-5 
5'0 
5'2 
5'4 
5'3 
7-3 
Ratio of latter to length 
0-23 
0-21 
0-21 
Diameter at annulus . . 
17 
2-0 
2'6 
2'5 
27 
3'0 
3'0 
