158 
DIENER : TRIAS OF THE HIMALAYAS. 
stratigraphically younger than the lower lias with Agassizeras globosum. 
The results of the detailed palaeontological investigation of the faunae 
from the valley of Utcubamba must be awaited before our uncer- 
tainty about the exact position of the South American beds with 
Pseudomonotis ochotica can be removed. 
We have become acquainted with a wide extent of the Indian 
Triassic fauna from the province of Herat to New Caledonia. Over this 
large area the successive faunae were distributed uniformly and had the 
same vertical range. But although the sediments were once continuous, 
a tolerably complete and connected account of their succession can only 
be constructed for the Himalayan region. In this district we have an 
uninterrupted development of Cephalopoda, which enables us to decide 
the enigmatical question as to the habitat of some cryptogene types. 
It has been shown that Xenodiscus ranges from Permian into Lower 
Triassic strata, undergoing several modifications, among which the most 
typical genera of Lower Triassic ammonites might be found. The most 
important phylum of Triassic ammonites has its root in the Indian 
genus Xenodiscus Waag., but Xenodiscus, Xenaspis, Ophiceras, Meeho- 
ceras are all so closely allied at the commencement of the Mesozoic era, 
that it is barely possible to point out a distinct ancestor to every 
Triassic genus within this stock of radicals. 
Meekoceras itself is probably a descendant of Ophiceras, more parti- 
cularly of the type with a narrow umbilicus, which is represented by 
0. Sakuntala. Another branch of the genus Ophiceras is Flemingites, 
an intermediate shape between the two genera, Fl. proenuntius, having 
been described by Freeh. But with equal reason some other species of 
Flemingites might be referred to Xenodiscus, as is demonstrated by the 
remarkable agreement of Flemingites radiatus Waag. with Xenodiscus 
plicatus Waag. 
An important branch of discoidal ammonites with adventitious 
lobes certainly originated from Meekoceras. Hedenstrosmia is also 
connected with this genus most intimately by Clypites Waag. (group of 
Hedenstroemia lilangensis Kr.). Types specialized more strongly are 
Aspenites Hyatt and Pseudosageceras Dien., which is connected with 
Hedentroemia by a fragmentary species from the Meekoceras beds of 
Spiti. 
Proavites, Proptychites , Beyrichites are all probably descendants from 
Meekoceras which have retained the originally smooth shells. But 
( 359 ) 
