Echinoid Radioles. Cidaris Hausmanni. 
203 
The numbers of ribs and pustules are estimated at the level of the greatest 
diameter. When variation occurs on different faces, the finer ribs contain the smaller 
pustules. The ribs of E 9514 are smooth, perhaps worn, so that the pustules, 
if they existed before petrifaction, can not be counted (compare Lauper, 1865, f. 
13 a, g). The pustules are normally rounded, borne on the ribs, and subequal 
on each rib. In E 9517 the ribs are thin, equally spaced all round, and the pustules 
are spinelets with a rake distalwards; this specimen approaches most nearly Lausr’s 
figures 13 0b, f, and Kuipsre’s figure 14 g. There does not appear to be any 
definite correlation between the size or spacing of ribs and pustules and the axes 
indicated by the oblique base: no. finer ornament on a possible adoral face, no 
intensification of lateral ribs. Owing to the approximate equality of ribs and pus- 
tules, the ornament has at first sight a regular appearance; but closer examination 
shows that a rib rarely passes from end to end of the shaft, and that when it 
does so, its course is usually curved. Often the ribs that are strongest at the distal 
end die out proximally (E 9517), often other smaller ribs appear in the middle of 
the shaft, especially in the more swollen forms, and often the ribs as they pass 
distalwards coalesce by twos or threes, bending to the right or the left. Thus the 
ornament is far from having the essential regularity of such a form as C. similis 
or even C. Waechteri, and this no doubt throws some light on the peculiarities of 
the microstructure. 
The base in all these specimens is oblique, but its most characteristic feature 
is the collerette: this is very short, and widens rapidly to a well-marked distal rim, 
which at first sight is liable to be mistaken for the annulus. The annulus scarcely 
projects beyond the collerette, but below it the base is greatly constricted, perhaps 
sometimes undercutting the annulus. Then the base swells out again, bead-wise, 
proximally, and is crowned by a small swollen acetabular margin. The general 
appearance is as though one had taken a base, fashioned in some soft material, 
and telescoped it towards the shaft, thus shortening and swelling each of its members. 
When the small acetabular margin has been worn away, the bead-like base itself 
may be taken for that margin, the slope from the annulus to the collerette may be 
confused with the slope of the base, and the collerette, as already said, may be 
mistaken for the annulus. 
The acetabulum shelves gradually to a central pit. Its margin, though oblique 
to the main radiole axis, is not so oblique as the collerette; therefore the tele- 
scoping, if one may so express it, has been more on one side. 
There is no crenelation on any structure of the base. A very fine longitudinal 
Striation can just be made out on the collerette in the best preserved specimens. 
The micro-structure has been briefly described by Hrssr (1900, p. 228) who 
gives a diagram of it. From the almost imperceptible axial complex he shows a 
septum radiating to each of the outer ribs; and from each side of these main septa 
he sees short, more delicate septa, given off at regular intervals, at an angle of 
about 45°, passing towards the periphery, and abutting on the corresponding septa 
from the adjacent radiate septum. These side septa are drawn as regularly spaced, 
slightly curved, and united by regular straight trabeculae. 
The beautiful drawing by Mr. G. T. Gwitiiam (PI. XVI, fig. 448) is an accurate 
representation of part of an excellent cross-section (E 9518). While it recalls Dr. HEssr’s 
diagram, its details are very different. There are no main radiating septa, but a 
