Echinoid Radioles, Cidaris trigona. 228 
round grains, lying within the meshes; these may represent the carbonised remains 
of the stroma, which was of course greatly in excess of the stereom in such a form. 
Specimens from the Pachycardientuffe. — Brom (1903, p. 156) 
has found the radioles fairly abundant in this formation at the Seiser Alp. Their 
average size seems to be smaller, and the distal end is frequently either broken or 
rugose. They may represent a slight mutation, but the adherent matrix prevents 
close examination of the ornament, and no further differences are discernible either 
in the specimens at Munich or the two in the British Museum (E 4699). The 
chief measurements of the latter are: greatest length, 8°7 and 11°5 mm.; greatest 
sagittal diameter 47 and 5°2 mm.; _ greatest transverse diameter, 5°4 and 73 mm. 
Material from Bakon eS — The Cassian bed e4 of Section VI, Veszprém, 
has yielded two small specimens (Plate XIII, figs. 413—416). In both the distal end is 
more truncate than I have observed in any Cassian specimens. The smaller of the 
two (figs. 4183—415), which is the better preserved, has a flattened, concave, face 
of relatively greater width than any Cassian specimen, and in this respect contrasts 
still more with those from the Pachycardientuffe. On this face are seen the vertical 
walls of the prismatic tubes, but there is no imbrication. On the back the pustules 
are in distinct longitudinal rows. In the larger specimen the flattened face is obscured 
by matrix, and on the back (fig. 416) the pustules are coarser and irregular. 
The following are measurements in millimetres : 
Greatesiglenciimeryee-§ A iPoiy) .0) tee side 0 60 
Greaesinsaritialmcianieteins es eon eee ne.O 30 
Greatest transverse diameter. . .... . 39 40 
Length of flattened face . . . 35 48 
Length from acetabulum to distal ond of fepale IGS Lea 
Length from acetabulum to top of collerette . O04 i 
Diameter OheannUliSnwey 4 Yl sao). wena 078 15) 
Thus the ratio of greatest width to greatest length is 0°84 and 066. 
It is possible that these Bakony specimens .represent a local variety or a 
mutation; but till other specimens have been found with a similar structure, it 
would not be wise to propose a new name. 
Relations of the species. — Lause was doubtless correct in referring 
to Cidaris trigona the radioles on which Cornauia (1848) based his C. imbricata 
and C. truncata. These are quite characteristic of the larger and smaller sizes 
respectively. In Cornauia’s fig. 3b, the imbrication of the concave face in C. truncata 
is much closer than in equal-sized specimens of C. trigona; but, to judge from 
his description, the closeness is greatly exaggerated in the figure. 
IKOECHLIN-SCHLUMBERGER (1855) regarded Cidaris trigona as only a variety of 
C. dorsata. We have already seen that the complete series of C dorsata, whether 
from youth to age or from adoral to adapical, runs on other lines than those followed 
by the series of C. trigona. Apart from this, the micro-structure of the two forms 
is perfectly distinct. 
QueEnstept (1875), while maintaining the species, placed it next his Radiolus 
crumena (p. 195) of similar colour and appearance. The unique holotype of that 
species, in the Geological Museum, Tiibingen, owes much of its peculiar shape to 
