ov 
Cidaris trigona, Diadematoid Radioles. 22 
Diadematoid Radioles. 
Although Hessr (1900) has described all the Cassian radioles as modifications 
of the Cidaris type, this cannot be taken to mean that all belong to genera of 
Cidaroida; in fact the radioles of such admitted Diademoids as. Acrosalenia and 
Hemicidaris are also of the Cidaris type, and the radiole of Diademopsis Heeri 
from the Lower Lias is described by Hesse (1900, p. 250) as approaching the Cidaris 
type in many respects, notably in having no axial canal, but an axial complex 
merging into the radiate septa. Now, certain of the Cassian radioles seem to be 
much closer to the normal Diadema type than do any of these; they have a large 
axial lumen, separated by a distirict layer (the «Axialscheide» of Hessr) from the 
outer layer of radiate septa. The septa, too, are more regular and stouter than 
is usual in the Cassian Cidaroids, and crop out on the surface so as to produce a 
clear and regular linear ornament. The cross-section of Cidaris flexuosa as 
represented by Hesse (1900, p. 231, f. 2) serves as a general diagram of this type 
of structure, though in the section of that species now before me the trabeculae 
seem to alternate in position and the septa to bend in slight zigzag fashion from 
one trabecula to another, so that the enclosed meshes form radiating series of 
elongate hexagons. Further, I should not describe the cortex as «not preserved», 
but as «non-existent», at least over the greater part of the shaft. 
To this type of structure we have already recognised a tendency, either in 
the apparent resorption of the axial complex, or in the definite connection of the 
outer longitudinal ornament with the vertical radiate septa; and it may well be that 
some of the species hitherto described were not true Cidaroida. At any rate it 
seems most probable that those now to be discussed represent primitive Diademoida. 
To the Cassian species of this group the following names have been applied: 
Cidaris flexuosa Mtnst. (1841, p. 44), C. cingulata Mobwsrt. (1841, p. 44), C. linearis 
Mtnst. (1841, p. 45), C. Brandis Kursr. (1845, p. 269), C. Meveri Kutpst. (1845, 
p- 270), C. bicarinata Kursr. (1845, p. 272), and perhaps C. Petersi Laur 
(1865, p. 284) and C. undulatus Quenst. (1875, p. 199). All these, except the last, 
agree in possessing a distinct longitudinal striation; and this, in the type-specimens 
of C. flexuosa, C. cingulata, C. Brandis, and C. Petersi, is traversed at right angles 
or obliquely by coarser ridges, which are absent from the type-specimens of Cidaris 
linearis, C. Meyeri, and C. bicarinata. The former species may therefore be 
considered first. 
Between C. cingulata and C. flexuosa the only difference that can be gathered 
from Muinster’s diagnoses is that in the former the cross-ridges are «in ziemlicher 
Entfernung». but «sehr nahe stehende» in the latter. Measurements are not given, 
but one learns from Mobnsrer’s figure that in C. cingulata the ridges were at most 
0.84 mm. apart. In undoubted specimens of C. flexuosa before me [B. M. 36488, 
and 36510] the distance varies from 0°7 to 0°83 mm. Laue therefore was doubtless 
justified in merging the two forms under one name; he chose the name C. flexuosa, 
that being the better established species, and although this name succeeds C. cingu- 
lata on Miwsrer’s page 44, any attempt to reverse Lausr’s choice would be harmful 
and unnecessary. 
Resultate der wissenschaftl. Erforschung des Balatonsees. | Bd. 1. T. Pal. Anh. 15 
