Echinoid Radioles. Anaulocidaris. 
143 
shaft, hovvever, this Ornament can scarcely be distinguished, except in so far as thc 
minute structure of the stereom appears under favourable lighting; it is doubtful if 
it ever was more conspicuous in this specimen. On the base below the annulus 
it is slightly more visible. On the collerette it exists as distinct though fine striae, 
about 12 of which go to 1 mm. 
The collerette extends 3 mm. beyond the annulus, and is bounded by a faint 
but definite ridge, beyond which is a very slight contraction of the body of the 
radiole. In addition to the change of Ornament at this line, some specimens show 
a change of colour (much more marked in A. Bucht) probably due to the greater 
density of the base. Many shafts are broken off just here, while others are crushed 
just beyond the collerette ridge. This indicates the less solidity of the shaft, which 
may have contained actual cavities. In this connection it is to be noted that the 
extreme distal margin of this radiole thickens slightly, to about 0.5 mm., and is 
marked right along the distal border by a distinct though shallow groove, which 
is also visible in other specimens of about this size and shape. 
Specimen b differs from a chiefiy in being more curved. If the radiole be 
laid, with its inner face downwards, on a flat surface, the summit of the convex 
curve is at a height of 2.5 mm. above that surface. This is at the thickest part 
of the shaft, so that the concave curve of the other face is far less, and is at 
0.4 mm. above the fiat surface. This radiole is a little longer and wider on the 
left, but the asymmetry is not so marked as in a. 
The slope of the annulus is as in a. The rim of the acetabulum is slightly 
swollen, then comes a slight swelling between the rim and the annulus, then a 
rising up to the annulus. The whole of the base to the distal edge of the collerette 
is of a darker brown than the shaft; on the inner face a wide crack follows the 
rim of the collerette. There is no distal groove. 
Striation can be detected on the collerette, but elsewhere is only visible at 
the distal border of the adoral face; here are well-marked striae, or sulci, about 6 
to TO mm., but not quite equal in width. The adapical surface at this end shows 
traces of small pustules. Both these types of Ornament are faintly reminiscent of 
the radioles known as Cidaris alata and allied forms. They are to be seen in 
some of the other remiform radioles. In some (e. g. d) the pustules appear as 
slight elevations between the striae, which latter gradually increase in size and 
length nearer the distal margin. 
Specimen c, which is thinner than the others. partly because it is crushed, 
shows the striation very plainly over the whole adapical face and the distal half 
of the adoral face, but less plainly, in its proximal half. No collerette can be 
distinguished, but the striae Start at the annulus and increase in width and intensity 
towards the widest part of the radiole, thence decreasing in width towards the 
distal margin, where they are 10 to TO mm. At the distal border of the adapical 
face the ridges show slight irregularities, which, however, are not so definite as to 
form pustules. In the absence of a collerette, the crushing extends right up to 
the annulus. 
The measurements and outlines of specimens e, f, g, and h, show the forms 
and sizes of the larger remiform radioles. The considerable Variation in the develop¬ 
ment of the collerette is again exemplified by the fact that in two radioles of nearly 
