88 Triassic Echinoderms of Bakony. 
development between the similar structure in Archaeocidaris and the upright inter- 
locking suture of later Cidaridae, or, in the words of Prof. Torngutst, «eine letzte... 
verschwindende Eigenthiimlichkeit der mit verschiebbarem Panzer versehenen palaeo- 
zoischen Cidariden», so would I maintain that the bevelled sutures between the 
interambulacrals of Miocidaris are a stage between the similar sutures of Archaeo- 
cidaris and the smooth upright sutures of later Cidarids—another inheritance from the 
flexible test of Palaeozoic ancestors. But if this be so, the direction of imbrication 
must be the same. The hypothesis of a progressive evolution in this character is 
confirmed by the fact that the structures above described appear to be most definite 
in Archaeocidaris, rather less so in M. Keyserlingi, still readily seen in M. Cassiani, 
but less marked in M. planus and the other Raiblian Miocidaris. 
According to SpanpeEL (loc. cit.) the ridge serves as a stop («Widerlager») for 
the adjoining plate; but this view is inconsistent with the existence of a ridge on 
both upper and lower margins. There is more probability in the opinion of Torn- 
guist, that the ridge merely marks a groove for the attachment of the uniting 
ligament, on which view the presence of a ridge would indicate greater rather than 
less flexibility. 
Comparison of the direction of imbrication in Miocidaris with the various 
directions in which Tornouist has indicated it in Archaeocidaris shows the differ- 
ence between a form with two columns of plates in the interambulacrum and one 
with four columns, In the latter case the imbrication of the transverse sutures is 
adapical; but the resultant of the combined imbrication of the oblique sutures is 
from the interradius towards the radius, while on the interradius itself the imbric- 
ation is nil or indeterminate. In forms with only two columns the imbrication of 
the transverse sutures remains as before, but the resultant of the oblique sutures 
is a similar meridional imbrication in the same adapical direction; imbrication at 
right angles to this is confined to the adradial sutures. (See text-fig. 7, p. 60). 
This imbrication, or at least flexibility, of the interambulacral sutures appears 
a general, if not a universal, character in Miocidaris. In Triadocidaris on the other 
hand, I have noticed it only in 7. praeternobilis and in some plates of 7. immunita, 
where the transverse sutures are slightly oblique and grooved. In 7. persimilis the 
sutural face is vertical or very slightly oblique, with a faint median depression. It 
is, no doubt, on account of the less flexible union that complete interambulacra are 
more common in Triadocidaris than in Miocidaris. T. praeternobilis, as being the 
latest in the series, is perhaps the last species in which one would have expected 
to notice this apparently primitive structure. There is, however, good reason to 
suppose that the structure was carried on into the Diademoids, and T. praeternobilis, 
as we have seen, is distinctly Diademoid in its ornament. In this feature then, as 
in others that have been noticed, there seems to be a divergence of evolution, 
flexible sutures persisting in one series, but changing into rigid sutures in another. 
Miocidaris in Bakony. — To this genus are referred the following 
forms: — From the Cassian beds of Cserhat, a doubtful species, designated «, and 
another rather more like M. verrucosus, and designated f; from the Raiblian of 
Jeruzsalemhegy and Cutting I on the Veszprém-Jutas Railroad, M. verrucosus n. 
sp., M. planus n. sp., and an uncertain species designated 7. From Cserhat there 
also comes part of an ambulacrum, doubtfully referred to this genus, and designated 6 
