XI. Balanocrinus. 395 
Measurements of cirrus-facets in millimetres :— 
K 21984. E21982. E.21978. E 22027. 
Mean diameter of columnal., 7°65 8-2 91 9-4 
Wadthvor facet: os.. acs 55ee. 2:0 oy 2-75 2:5 
Radial diameter of facet .... 16 18 16 2:0 
Distance of axial canal from 
OUCEPAMATSING sere iene sass 1:0 115 1:2 a ID. 
The cirrus-notch in the hypozygal varies greatly in depth. 
Sometimes it is a slight almost V-shaped notch in the 
margin. Sometimes a channel, gradually shallowing, 
* stretches down the radius over two or even three columnals. 
How far this appearance is due to pressure after burial 
is uncertain, but it is worth noting that in E 21989 the 
granular ridge of the hypozygal side-face continues across 
such a channel. A characteristic form is seen in some well- 
preserved specimens (é. g., E 22027, Fig. 4; E 21978) ; as 
seen from the side it is of roughly four-sided outline, and 
occupies the upper two-thirds of the side-face; the shorter 
vertical sides approach one another slightly as they pass 
downwards, the upper edge is clearly marked, and is sharply 
bent inwards, corresponding no doubt to the angular inner 
margin of the formerly apposed cirrus-facet ; the floor is 
marked with two indentations, one above the other, and 
presumably corresponding with the first and second cirrals. 
In E 21989 three such indentations are seen in succession, 
and the dividing elevations can be distinguished from the 
continuations of the granular ridges previously mentioned. 
The remains of Cirri are rare. In only one or two cases 
is a cirral ensconced in the hypozygal notch or lying close 
by; in no case is a cirral still attached to the facet. In 
E 21989 a single cirral lies on the joint-face of the hypo- 
zygal. Its joint-face is a broad ellipse with one side 
flattened ; the long diameter is 1°75 mm., the short one is 
1:3 mm.; the margin is slightly raised ; the fuleral ridge 
bisects what would have been the ellipse and passes round 
the axial canal, widening more to the elliptical boundary 
of the joint-face. Since on the facet the straight side of 
the fuleral ridge is the outer side, it may be inferred that 
the flattened side of the cirral was outermost, and that the 
curved side rested in the hypozygal notch. The height of 
this cirral is about °8 mm. Whether the face described is 
proximal or distal cannot be decided. 
Alternicirration—The most interesting feature in this 
species is that diminution in the number of cirri at the 
whorl to which the name didactylus is due. The number 2 
