INDIAN TRIASSIC PROVINCE. 
159 
there is some probability of Meekoceras being also the root from which 
a large phylum of Ammonea trachyoslrnca originated. Forms of Meeko- 
ceras with a faintly developed ornamentation, which crosses the 
external part {M. Hodgsoni Dien.) belong to a genetic series leading to 
Sibirites in the upper division of the Lower Trias and to Acrochrodiceras 
in the Muschelkalk. 
But the most important Indian family of Triassic Trachyostraca, the 
Ceratitidoe, probably originated from Xenodiscus. This is pretty certain 
at least for the group of Ceratites circumplicati {Hollandites). Ceratites 
pumilio, the oldest representative of the genus, agrees with typical 
species of Hollandites in the shape of its cross section and in the pattern 
of its sculpture, with Xenodiscus in the development of its sutures and 
in its comparatively wide umbilicus. 
The restriction of Tirolitidoe to the Mediterranean province during 
the Scythian period, emphasized by E. v. Mojsisovics in 1896, has not 
been confirmed by later researches, but their sporadic appearance clearly 
proves them to have been immigrants from the Mediterranean region, 
not autochthonous elements, such as the Meekoceratidoe and Xenodiscidos. 
Dinarites also became independently developed within the Mediter- 
ranean and Boreal provinces, but cannot be regarded as an ancestor of 
the Indian Ceratitidce. 
The Indian Lower Trias is entirely deficient in Arcestoidea, which 
make a sudden simultaneous appearance both in the Himalayan and 
Alpine Muschelkalk. The considerable temporary intermittence 
between Joannites and the Permian Cyclolobus makes a genetic connec- 
tion between those two genera questionable. 
A second stock of cryptogene types, the Haloritidce, which were not 
known to E. v. Mojsisovics before the carnic stage have been 
discovered recently in the Muschelkalk, where Smithoceras is a peculiar 
representative of this family. This fact proves the Haloritidce to be 
an endemic element of the Indian province. But the problem of the 
habitat of Haloritidce during the ladinic and lower carnic periods 
still remains undecided. 
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