THE PERMO-TRIASSIC BOUNDARY. 
51 
character of the cephalopod fauna is what we should expect to find in a 
Mesozoic horizon, the overwhelming majority of the ammonites being 
provided with ceratitic sutures. This character is not exhibited in any 
Ferniian cephalopod fauna hitherto known. 
Among the genera of ammonites Meekoceras^ and Ophiceras are in 
commoi\ with the fauna of the Triassic Meekoceras beds. Proptychites 
and Prosphingites are Triassic genera. In the Meekoceras beds of Idaho 
species of the Ophiceras bed in Spiti are associated with an undoubtedly 
Triassic fauna. Among those species which have been quoted by J. P. 
Smith •'- three are probably identical with Himalayan forms, namely : — 
Ophiceras cf. Sakuntala Dien. 
„ cf. gibbosum Griesb. 
Meekocemf cf. Hodgsoni Dien. 
Two other species of Ophiceras are very nearly allied to Indian ones, 
namely, Ophiceras Spencei Hyatt et Smith to 0. ptychodes Dien., and 
0. Dieneri Hyatt et Smith to 0. demissum 0pp.'' 
All the numerous types of Palaeozoic brachiopods, which are the 
predominating and most characteristic element both in the Productus 
Limestone of the Salt Range and in the Ruling shales of the Himalayas, 
are completely absent from the Otoceras beds. There is no stratigraph- 
ical break in the uninterrupted sequence of beds, which in the Hima- 
layas connects the Permian and Triassic systems, but there is a distinct 
paiseontological break or hiatus at the base of the Otoceras beds. In 
the Himalayan region there is certainly no gradual shading-off from a 
Paloeozoic to a Mesozoic marine fauna through an intermediate group, 
but a sharply defined limit, which none of the characteri ,tic species of 
Permian brachiopods transgresses. This absolute distinction between the 
brachiopods of the Ruling shales and of the Otoceras beds is so sharp 
that the limit bettveen the two faunae offers itself as the most natural 
boundary of the tivo systems. 
I must object strongly to Noetling's criticism upon the importance 
of the absence of the Palaeozoic brachiopod fauna from the Otoceras 
1 Noetling's repoi't of the absence of tlie genus Meekoceras from the Otoceras 
stage has turned out to be incorrect. 
2 J. P. Smith : The stratigraphy of the Western American Trias, 1. c, p. .394. 
3 A. Hyatt and J. P. Smith : Triassic cephalopod genera of America, 1. c, pp. 118, 
119. 
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