Echinoid Tests, Cidaroida, —__ _ 85 
ancestor of one in which they are circular and distinct. But if the species with 
confluent scrobicules occurs at an earlier horizon than the other, obviously it cannot 
be its descendant. Are the two species, on that ground alone, to be placed in 
different genera? If the generic idea is to be restricted to a single line of descent, 
as is the tendency with workers in some groups, then the answer is «yes». But 
it does not seem to me that our knowledge of the Echinoidea, or at any rate of 
the Triassic Echinoidea, is sufficiently complete to render such a restriction pract- 
icable. I content myself, therefore, with pointing out that the separation of genera 
by the shape of their scrobicules could be justified only by some such determination 
of phylogeny. 
The denticulation of the adradial suture, though introduced by DorDERLEIN into 
the diagnoses of his group 5 (Cidaris subcoronata) and of Triadocidaris, was omitted 
from his diagnosis of Miocidaris, whence it might be inferred that the bevelled 
surface was supposed by him to be smooth. In M. cassiant, however, there are denticles : 
so that whether this be mentioned in the generic diagnosis or not, must depend 
solely on the value attached to the character. It is possible to imagine an oblique 
flexible adradial suture without denticulation, either because denticles have not been 
developed or because they have become obsolete. I should hesitate to remove a 
species from the genus on such grounds. What may be the case in some of the 
Liassic representatives of the genus, I do not know; but, so far as the species 
herein referred to are concerned, the question hardly arises, for there is only a 
single interambulacral that has a smooth bevelled surface, and even that appearance 
may be due to weathering. There is, however, some evidence for an evolutionary 
cycle. ‘Thus, the oldest species, Miocidaris Keyserlingi (Geinitz), sometimes has an 
irregular denticulation (seen in Brit. Mus. E1121), while SpanpeL (1898, pl. XIII, 
f. 4b) has figured broad and short, but more regular denticles; since, however, 
DoeDERLEIN (loc. cit.) denied the existence of such denticulation in this species, and 
since no other author has mentioned it, very probably it was not always developed. 
The interambulacrals from the Wellen-dolomite of the Schwarzwald which QuensTEpT 
(1875, pl. LXVII f. 115) referred to Cidaris grandaeva, are denticulate, while the 
same feature is well marked in the St. Cassian species and in Miocidaris verrucosus 
from Bakony. In M. planus, however, from the Raiblian of Bakony, the denticles 
are very faint, and in an unnamed plate, as already mentioned, they seem to have 
disappeared. All these facts therefore have been introduced into the revised diagnosis 
in the phrase «usually if not always denticulate». 
It is quite possible that the Bakony species indicate a divergent evolution, 
M. verrucosus leading to the stereosomatous Cidarid, Plegiocidaris, while M. planus 
may be more closely connected with an early Ectobranchiate such as Eodiadema. 
It is necessary now to justify the relegation of Eotiaris to the synonymy of 
Miocidaris, especially as some of the Bakony fossils would have been referred to 
that genus had it been retained. The genus was proposed by Lampert (1899) for 
the reception of Cidaris Keyserlingi Gerinitz, removed by him from Kocidaris in 
which it had been placed by most authors. In 1900 (op. cit., pp. 38, 39, 40) 
Lampert also referred Cidaris grandaeva to Eotiaris provisionally, and pointed out 
in what way the genus differed from Triadocidaris, Microcidaris and Plegiocidaris. 
Nevertheless he attempted no diagnosis, but presumbly adopted for it DorpERLEIN’s 
diagnosis of Eocidaris (1887, loc. cit.), since that was based solely on C. Keyserlingt. 
