222 Triassic Echinoderms of Bakony. 
In taking these measurements the flattened side has been regarded as vertical. 
The ratio of sagittal diameter to length varies from 0°32 to 0°61, and these extremes 
occur together near the middle of the series; their mean is 0°47, and the average 
is 0'42. The ratio of transverse diameter to length varies from 0°5 to 0°71, and 
these extremes also occur close together; their mean is 0'6 and the average is 
0:59. The ratio of the total height of the base to the diameter of the annulus 
varies from 0°46 to 0°69, the mean being 0°57, and the average 0°56. 
The Micro-structure has been briefly described by Hesse (1900, p. 229) 
in conjunction with that of Cidaris Wacchteri. There is really considerable differ- 
ence between the two; in fact that of C. trigona is exceedingly peculiar, so much 
so that one can scarcely recognise a cross-section as representing an Echinoid 
radiole (Plate XVII, fig. 452). The axial complex occupies a very large part of the 
cross-section, about two-thirds of the total diameter. It consists of thin-walled 
polygonal meshes, irregular in shape and size, but usually large. Towards the 
periphery, the walls of these meshes merge into rather thicker, widely but irregul- 
arly spaced, radiating septa, sometimes dichotomous, and joined by a few thin 
trabeculae at irregular intervals. At the extreme. circumference the septa thicken 
suddenly and are united by an outer layer, which is of about the same thickness 
as the inner parts of the septa, but thickens to form the pustules of the surface. 
The septate layer is not always equally developed all round, but on the flattened 
face of the shaft can often scarcely be distinguished from the polygons of the 
axial complex. The appearances remind one of a section across one of the Palaeozoic 
Trepostomatous Bryozoa, such as Diplotrypa, so much so that | laid aside as 
useless the first thin section that was made, supposing the radiole to have been 
invaded and in great part absorbed by some encrusting Bryozoon or Hydrozoon. 
Further examination of sections and weathered surfaces at last permitted the following 
interpretation. The whole mass of the shaft is composed of prismatic tubes, between 
which others arise at irregular intervals. These tubes are traversed at unequal 
distances by trabeculae or by cross-partitions, sometimes flat, sometimes curved. 
Around the main axis, and towards the flattened face of the shaft, the tubes approach 
a vertical position, but the outer ones gradually bend over till their ends lie at 
right angles to the outer face of the sides and back of the shaft. Here they are 
sealed by the thin pustulate cortex. 
Applying these facts to those already learned about the surface ornament, we 
infer that in the younger radioles the prisms are nearer the vertical throughout, 
and the high angle at which they strike the outer surface tends to produce an 
imbricate ornament. This is most obvious on the flattened face, where it persists 
longest, so that examination of this face with a strong lens (X 16) reveals the 
almost vertical walls of the prisms, forming pillars between the imbricate lines of 
their outcropping ends; between the pillars may also be seen occasional cross- 
partitions or trabeculae. Whatever may be the case on the sides of the shaft, the 
prisms always strike the distal crown more or less at right angles, so that the 
ornament there is never imbricate. The similarity to a massive Bryozoon stock is 
thus seen to govern the whole structure of the shaft, except for the fact that on 
the surface the prismatic tubules are closed by a cortex. 
The section is obscured in parts by agglomerations of small, densely black, 
