Echinoid Radioles, Anaulocidaris. 149 
plane of the bevel; 2. a less clearly marked bevel on the NE. and NW. sides, 
most marked towards the NNE. and NNW. angles; 3. a rising up to form the 
handle, steeply on the north side, but gradually on the E. and W. sides of it, thus 
forming a couple of broad ridges that pass towards the E. and W. corners; 4. on 
the S. side of the ridges, the surface slopes gently down to the margin, but immed- 
iately S. of the handle the slope is almost vertical to the blade and is slightly 
hollowed in a transverse sense thus producing two broad ridges running from the 
handle towards the SSW. and SSE. corners. The four ridges that run from the 
handle to the E. and W. and SSE. and SSW. corners must be distinguished from 
the two ridges that in A. Buchi run to the NNE. and NNW. corners. The former 
are homologous with the sides of the handle as seen in the spatuliform radioles; 
the latter, as we shall see later, have a different origin. 
The base in this specimen is clearly distinguished from the cream-coloured 
shaft by a brown tint. The curves of the handle are continued over the collerette, 
which, however, is marked off from the handle by a sudden, clean-cut, but very 
slight descrease of diameter, the width being 3°6 mm. and the thickness 2°4 mm. 
Further, the striae on the collerette, though very fine, are more distinct. The 
collerette is not so easily distinguished from the annulus, but its height may be 
estimated as0°6 mm. on the adapical side and0O’4mm. on the adoral. Thus it is 
very short in proportion to the width of the base, and its distal magin is not quite 
parallel to the annulus. The course of this margin and of the annulus will be 
better understood after the acetabulum has been described. 
The acetabulum is a hollow of transversely subelliptical outline, the ellipse 
being slightly flattened on the north or adoral side. The acetabular rim is well- 
marked and separated by a slight groove from the rest of the base. The external 
measurements of this rim are: width 1°5 mm.; thickness 1°2 mm. The rim does 
not all lie in one plane, but, as seen from the proximal end of the radiole, appears 
to sink on the N. and S. and to rise on the E. and W. This deflection is slight, 
and, if it be ignored for the moment, the plane of the acetabular rim may be 
described as sloping southwards at an angle of about 45° to the general plane of 
the blade. From the acetabular rim the base slopes, with a convex curve, to the 
annulus. On the north side, however, the slope is steeper than on the south; in 
other words the base is flattened on the north side. 
The annulus is a rounded ridge, more clearly raised on the side of the ace- 
tabulum than on that of the collerette. It is deflected from the imaginary plane at 
45° to the blade in the same way as the acetabular rim, but to a far greater extent. 
Thus the E. and W. sides rise up towards the proximal end of the radiole, while 
the N. or adapical side is depressed towards the blade. The shape can best be 
compared to the brim of a felt hat turned up on one side more than on the other. 
We are now in a position to consider the complicated ornament of the shaft. 
This consists of fine striae and the ridges between them. On the inner face these 
are more clearly seen. Starting from the bottom of the handle, where it joins the 
collerette, they radiate to all the sides. Since the adapical side of the handle is 
morphologically part of the outer, and primitively adapical, face of the shaft, one 
is not surprised to se ethat the striae which go to the S. margin pass over it and 
then radiate from that margin over the outer face to the N., NE., and NW. margins; 
those at the sides are approximately parallel to the SE. and SW. margins. What 
