OF SOUTHERN INDIA. 251 
proposed for a liassie discoidal shell, composed of quadrangular whorls, carinated and 
more or less crenulated on the upper and lower edges of the back, on which the strie 
of growth are insinuated backwards. In my paper on the Gastropoda and Acephala 
of the Hierlatz-strata (Sitzb. Akad., Wien, 1860, Vol. XLIITI, pp. 180, ete.), I have 
described several liassic species, and at the same time I have endeavoured to prove, 
that the peculiarities of these shells entitle them to be classed under a genus, 
distinct from Straparolus, (Euomphalus, olim). Farther details may be found in that 
paper. The oldest forms very much resemble Straparolus in being above slightly 
elevated or plane, like Straparolus tuberculosus, dOrb., but they strictly retain 
the angular form of the whorls with an obtuse back and the two marginal keels, the 
lower of which corresponds with the umbilical, and the upper with the peripherical 
edges of Solariwm. Only in this way is it possible to make a correct comparison 
between the two genera. 
Species, which correspond in all the above mentioned characters with Discoheliz, already begin 
in the Silurian deposits, and seem to be most numerously represented in the Lias. They gradually 
decline in number from that time. Iam not aware of a single species, which has been described 
from the cretaceous rocks of Europe, nor have I anything to contribute from India. The two 
species, Straparolus subplanus, Gabb, and St. lapidosus, Morton, sp. (Delphinula idem) from the 
Alabama cretaceous deposits may, however, possibly belong to Discohelix (Journ. Acad. Nat. Se., 
Phil., 2nd Ser., Vol. IV, pp. 299-300, pl. 48, figs. 4 and 5). The former seems to have had the last 
volution partially detached from the rest, a ease which is commonly found among the eocene Bifrontia. 
Tertiary species appear to be equally rare. The Ordis roted/a, Lea (Cont., p.123) is a true Discoheliz. 
Michelotti’s Bifrontia Rochettina, (Descr. Foss. Terr. mioc. de I’ Italie sept. 1847, p. 172) is 
stated to be a discoid shell, with two slightly crenulated keels above and below on the periphery of 
the last whorl and a quadrangular aperture; these characters evidently recall the form of a Discoheliv. 
The operculum of the Discoh. zanclea, Phil. sp., is conically elevated, composed of numerous 
volutions ; it resembles that of the Zorinia-group of Solarium, and of the SzLiq@variD&. We are 
indebted to Deshayes (loc. cit., pp. 678, &c.,) for having pointed out the mistakes, into which H. and 
A. Adams, Gray and other subsequent authors, had fallen, when they declared Philippi’s living* 
species, Bifrontia (Discohelix) zanclea, which he only doubtfully referred to Bifrontia, to be identical 
with that genus. Deshayes says, that one has first to examine the fossil species of Bifrontia, to 
be certain of the distinctions, which exist between them and the Discoh. zanclea, Phil. sp. 
In fact the growth of the shel! appears to be a totally different one. Let us take for comparison one 
of the species, which are otherwise closely allied to Discohelix, as, for instance, the Bif. amonoides, 
Desh., we can always notice that the strie of growth are in Discohelix insinuated backwards, while 
in Bifrontia they are always curved forward. 
Another living species, the De/phinula (Liotia) evoluta, Reeve, for which H. and A. Adams 
proposed the sub-generic name J/aira, (Gen. I, p. 405,) may also be considered as a Discohelix. The 
shell is perfectly identical with the typical, liassic discoidal forms, Discohelix orbis, Reuss, sp., and 
other species. 
Hornes (Denksch. Akad., Wien., 1855, pt. IT, p. 42, pl. 1, fig. 6), when introduc- 
ing his new genus Platystoma (not idem, Klein, 1753, and not to be confounded 
with Platyostoma, Conrad, Hall), draws attention to several species, which we have 
referred to Discohelix, being probably incomplete specimens of the same genus, as 
* H. and A. Adams (Gen. I, p. 244,) state, that living specimens of this species have been dredged off the 
coast of Madeira by MacAndrew. 
