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

H0PLITE8. 17 5
The nature of the external margin, tl.o form of the shell and tl.« hutur* i.r,-*
have been described so often that it would be superfluous to ent*r here
details.
- The sculpture of Neocomites neocomiensis and Neocomites nivalis n.
agrees exactly with the description outlined above, while Neocomites mcrrdanm
and Neocomites indomontanus show slight deviations, in so far as all tbe rihe
of the fascicles are branched, with the result that the number of ribs increase
considerably on the outer portion of the volutions. This feature recalls Holies
cyptoceras d'Orbigny, a species which cannot be referred to the present group
in consequence of the discrepancy of its suture-line.
The group of Neocomites calliptychus consists principally of small forms with
rounded flanks, oblique umbilical walls and somewhat strongly sigmoidal ribs,
the points of bifurcation of which are situated at different heights. In one
form, Neocomites calliptychus, there is a feeble indication of small tubercles. The
suture-line is in general similar to that of the preceding group. It is, there-
fore, chiefly by the form of the shell, and of the more rounded or more ellip-
tical cross-section, that the present group is distinguished from the preceding one.
Neocomites Theodorii Oppel sp. and Neocomites indicus also exhibit a close
approach to the neocomiensis group. They possess sharp deeply cleft, nearly
filiform ribs ; the cross-section of their volutions is wedge-shaped and contracted
outward, the ventral furrow is very narrow, and is traversed by the rib6 in
larger specimens.
The ornamentation and structure of the suture-line assign also to the fourth
group, that of Neocomites odontodiscus, a place near Neocomites neocomiensis.
The character which differentiates this group and gives it a remarkable appearance
consists in the exceedingly broad, flattish and scanty ribs on the body-chamber.
Unfortunately several species belonging to this group are so badly preserved that
we have not ventured to define them specifically.
Of these closely related groups that of Neocomites neocomiensis d'Orbigny
appears to have the widest distribution. In Europe it is represented not only
by the well-known species whose name we have selected to designate the whole
group, but also by Neocomites castellanensis d'Orbigny sp., Neocomites heliacus
d'Orb. sp., Neocomites vicarius Vacek, Neocomites scioptychus Uhlig, Hoplites sp.
(Uhlig, Cephalopodenfauna der Teschener Schichten, PL VI, fig. 7), and Neocomites
perisphinctoides Uhlig. Amongst American species Neocomites Tenochi Felix and
perhaps also Neocomites Hyatti Stanton may belong to this group. Very little
can be said about the distribution of the remaining three groups. 1 Side by
side with the remarkable Neocomites odontodiscus may be placed the American
Hoplites Burckhardti Mayer-Eym., but nothing of the kind can be mentioned
amidst the European material. At first sight, Steueroceras transgrediens appears
to have a striking resemblance to Neocomites odontodiscus, but a closer
examination discloses the fact that the type of sculpture as well as the structure
1 The Fauna of the Knoxville beds. Bull. V. S. Geol. Survey, 133, 1896, part XVI. fig. 2, p.
a 2