174 
Triassic Echinoderms of Bakony. 
fication of the stereom that can be described as a cortex. Hesse (1900, p. 227) 
notes the absence of this «Deckschicht» or epistereom from all the St. Cassian 
radioles, and ascribes it to incomplete preservation. ln the case of Cidaris decorata 
his explanation is correct, for the structure is to be detected on a section now 
before me; but probably the cortex was wholly undeveloped in C. dorsata and 
C. alata. In its place C. dorsata possesses an outer layer of fine, close-set, and 
regulär radiate septa, united by regulär and closely spaced trabeculae; in a trans- 
verse section across the proximal half of a radiole from St Cassian, with a diameter 
of about 6’5 mm., this layer extends to a depth of about 0"4 mm. and contains 
about 48 radiate septa to the millimetre. Where pustules occur on the surface the 
septa fan out slightly and fresh ones are intercalated. Although the inner limit of 
this layer is far from following a regulär line, still the change to the inner layer 
is fairly distinct and rapid. The inner layer, which passes right to the centre of 
the radiole, consists of loculi varying in size and arrangement, but on the whole 
disposed in rows radiating from the centre; the loculi near the centre and towards 
the periphery are the smaller; nearlv all appear oblong, with the longer axis in 
the radial line. 
A similar section of Cidaris alata from St. Cassian (fig. 440) shows several 
points of difference. The inner layer is composed of more regulär loculi, and is 
therefore less distinct from the outer layer, into which it merges. There is an axial 
complex of quite irregulär loculi; the septa, however, do not radiate from this 
alone, but from a transverse line separating the inner and outer halves of the 
blade. Towards the periphery about 32 radiate septa go to the millimetre ; near 
the median transverse line the septa seem to be closer and thicker, as though the 
vanes were, from their first appearance, composed of denser stereom. 
If now we turn to the Raiblian forms of these two species, we find that the 
essential differences remain, but that each species has changed in a similar direction. 
The change in each case consists of an increase in size and irregularity of the 
loculi of the inner layer; thus, in C. alata poculiformis (fig. 441) the adcentral 
loculi of that layer now merge with the axial complex, and in C. dorsata marginata 
(fig. 439) the central loculi no longer retain any trace of radiate arrangement, but 
are as irregulär as those of an axial complex. The differences, as before, consist 
in the greater closeness of the outer radiate septa in C. dorsata, 40—44 to the 
millimetre, as opposed to 20—25 in C. alata; in the greater distinction between 
these and the inner layer in C. dorsata; in the direction of the radiation in C. alata, 
and in the denser stereom of its vane. 
The facts of microstructure, then, so far as they have been ascertained, confirm 
the Separation of C. alata from C. dorsata, and show that there is an internal as 
well as an external difference between the Cassian and Raiblian forms. 
The preceding discussion may be summarised in the following diagnoses. 
Diagnosis of « Cidaris » alata. — A Cidaroid in which the radioles 
have an irregulär microstructure, with axial complex, radiate septa irregularlv spaced 
and sometimes dichotomous, radiating from a median transverse line, and separated 
by irregularly spaced trabeculae; radiole-shaft normally of sub-lanceolate outline, 
differentiated into handle and blade, the former smooth or with faint longitudinal 
striae, the latter with pustulate Ornament varying in parts of the surface from 
smooth to ridged, or again to spinulose. All radioles, except a few circum-apical, 
