14 Triassic Echinoderms of Bakony. 
The diagnosis is modified from that given by Lampert (1900). Neumayr (1889) 
gave the further details: apical system unknown, peristome scarcely notched, general 
form depressed and like Pseudodiadema. 
The systematic position of the genus is governed by that of the genotype, 
which fortunately is fairly well known. Neumayr regarded it as a link between 
Cidaridae and Glyphostomes, placing it provisionally with the latter. Presumably he 
intended it for an Orthopsid, but he admitted that it might prove to be a Salenid 
if the apex were known. Mesodiadema was not mentioned by Grecory (1900); 
but Lampert (1900) and DeLtacr & H&rouarp (1904) have placed it in their Pedin- 
inae, while no one has ever proposed to place it in the Salenidae. 
For the sake of comparison with the Bakony forms, and to get a clearer idea 
of the general characters of the genus, the species that have been referred to 
Mesodiadema may be briefly considered. With the exception of M. Marconissae 
and M. Lamberti, the reference of these species is due to Lampert (1900). 
(1) M. Marconissae (DEsor sub Hemipedina). The best description is that by 
P. de Loriot (1882). From this we learn that the interambulacra are very wide, 
consisting of 10—11 plates in a column, each bearing a relatively inconspicuous 
tubercle, excentric towards the ambulacrum, with a very small mamelon and a 
wide, rather sunk scrobicule; that the whole extra-scrobicular surface is covered 
with very fine miliaries, a little unequal, close-set, and forming imperfect scrobicular 
circles; that the peristome is flush with the test, scarcely at all notched, and 
extremely small, its diameter not exceeding 0.22 that of the urchin. Der LorioL’s 
figures 1 and la are far from clear. In the enlarged figure 1b the extra-scrobicular 
miliaries are not close-set, and the scrobicular ring is more definite than the description 
leads one to expect; it further appears that the rings are contiguous but distinct, 
that the scrobicule is slightly sunk at its margin and rises gradually thence to the 
small mamelon. If the width of an interambulacral as drawn be taken as 100, then 
the height is 70—78; the distance of the centre of the tubercle from the adradial 
suture, 39; the width of the scrobicule, 31; the width of the mamelon, 9.5. 
Neumayr’s figure of the test seen from the side (though said to be «nach P. de 
LorioL») shows the scrobicules quite close to the adradial sutures. It would be well 
to have these small discrepancies cleared up. 
(2) Cidaris criniferus QurensteDT (1875, p. 156, pl. 67, ff. 99—100), Lias © u1 
Pliensbach, Wurteinberg, (= Toarcian). The evidence, however, is far from adequate. 
(3) Cidaris olifex QuenstepT (1875, p. 148, pl. 67, ff. 76—88), higher Lias 
a of Dusslingen (= Sinemurian). At the oral end of each interambulacrum, on the 
inner surface, is a thickened line representing the perignathic girdle. Thus the 
peristome slightly approaches pentagonal, but shows no gill-grooves. The adapical 
half of the test has 5 interambulacrals and 10 ambulacrals in each column [i. e. 
2 Amb. to 1 iAmb.], while the oral half has 6 or 7 interambulacrals, making 
therefore a total of at most 12 interambulacrals. Adapically and about the ambitus 
the main tubercles are slightly nearer the adradial margin, but adorally they grad- 
ually approach the interradius; adapically they become much smaller; they are 
perforate, «mit undeutlicher Strahlung», and, on the adoral half of the corona, have 
an incompletely developed scrobicule. Tubercles occur on the perradial tracts of the 
ambulacra ; in the adapical half of the corona they are small, and one is borne by 
each ambulacral; in the adoral half they are larger, and are borne only by every 
