partI.] Feistmantel: Cretaceous Genus Omphalia near Namcho Lake. 25 
Also those specimens figured in D’Orbigny and Coquand, and those recently described 
by M. Drescher (1. c.) have higher whorls. 
In the other dimensions our species agrees mostly with Omphalia Kefersteini, Munst. 
spec., to which also Omphalia suffarcinata, Munst. spec., is to he placed. 
With these our species’ is also otherwise related; but different by the two very well 
marked spiral ribs in each of the whorls, of which one runs on the lower part of the whorl, 
and the other in the middle of it, while in Omphalia Kefersteini, Munst. sp., still a third 
rib runs on the upper part of the whorls. 
I named the species after Captain Trotter, who has presented the specimens to our 
museum. 
As Omphalia as yet is known almost only from cretaceous, and mostly from upper 
cretaceous, we have to consider our form also as most probably of upper cretaceous age. 
Cretaceous rocks in the Himalayas are known with certainty still only from Spiti, de¬ 
scribed by Dr. Stoliczka as the Chikkim limestone in his paper on North-West Himalaya 
in Mem. Geolog. Surv. India, Yol. V, p. 116. But only several fragments of Kudistes and 
numerous Foraminifera were observed. 
From these fossils we had certainly to look upon the Chikkim limestone as a marine 
formation, while the beds near Namcho Lake with Omphalia were littoral or brackish. 
Some rocks of cretaceous age occur in the Kasia hills, near, but quite detached from, the 
eastern Himalaya. 
Natica species. 
From about the same locality are three other specimens of Gasteropoda; from the 
general form one can judge with much probability that they belong to the genus Natica, 
they are however imperfect just at the aperture, and none of them shows this portion suffi¬ 
ciently. The specimens are of a large size and all more or less compressed, as are also 
several of the specimens of Omphalia. 
We know Natica occurs in most of the formations, and it is therefore most probable 
that the specimen? under discussion are out of the same beds as Omphalia Trotteri, Fstm., 
t. e., from upper cretaceous rocks. 
Explanation of Plate. 
Figs. 1, las, 1 b .— Omphalia Trotteri, Fstm. Specimen with unknown locality, amongst the 
collections of the Asiatic Society of Bengal. 
Figs. 2—4.—The same species. Specimens sent by Captain Trotter, and collected near 
Namcho Lake, Tibet. 
