Ser. XV. HIMALAYAN FOSSILS, Vol. IV. THE FAUNA OF THE SPITI ...

species from the Spiti Shales :—
Himalayites Seideli Oppel sp. '
ai Icutianus n. sp.
11
Schlagintwetti n. sp.
n. sp. indet.
II
II
II
II
II
Hollaridi n. sp.
ventricosus n. sp. /
Stoliczkai n. sp.
HIMALAYITES, Uhlig. 1
umbo Strachey- Blanf ord.
depressus n. sp.
hyphasis Blanford sp. '
n. sp. indet. '
hoplitiformis n. sp. /
All the species of Himalayites are characterised by a widely umbilicated shell con-
sisting of rounded, frequently broadly depressed, and only slightly overlapping volutions.
The mode of coiling, particularly that of H. Seideli, recalls the genus Lytoceras ; the
umbilical wall of all the species is rounded and slopes down rather obliquely towards
the umbilicus ; m the adolescent and full-grown stages the height of the volutions is in-
variably less than their breadth.
In the adolescent and adult stages the sculpture possesses a very characteristic
feature : at about half the height of the flanks, individual ribs swell up into strong knobs
from which originate bundles of three to five branch-ribs. Between each two successive
tubercle-bearing ribs there are intercalated from one to three simple ribs. In the major-
ity of forms main and branch-ribs are disposed radially and take a straight course ; it is
only in isolated species that the ribs are slightly deflected forward or show a slight sigmoi-
dal curvature. On the other hand, the branch-ribs exhibit a fan-like disposition, the
anterior ribs of each bundle being deflected forward, whilst the posterior ones assume
a radial direction or even a slight backward inclination. T^he ribs extend across the
ventral face forming transverse or slightly arched, prominent ridges. Along t»he median
line they are slightly, although usually only just perceptibly, reduced ; this reduction
1 Pagos 1 to 132 of Professor Uhlig's Memoir, originally written in German, have been translated into
English by Mr. L. L. Belinfante. The English translation of the remainder is from a rough draft by Professor
P. Briihl, carefully rovised and largely re-written by Mr. E. Vredenburg,
i
B