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

HOPLITES.
The general type of ornamentation and the shape of the shell are similar
to the corresponding characters of Neocomites. Indeed, individual species pow^.v.
n sculpture which is hardly distinguishable from that of Neocomites neocomieiui* ;
such is for instance the case with Leopoldia paraplesia. Other species, such aa
Leopoldia aff. Arnoldi v. Koenen, L. Zitteli Uhlig, L. Karakaschi Uhlig, L. heterf/p-
tycha Pavlow, exhibit a slight tendency towards the formation of tubercles;
in others again the ribs gradually disappear from the flanks and become reduced
to obsolete traces in the vicinity of the external and umbilical margins. This
retrograde evolution of the ornamentation during the adult stage is most strongly
pronounced in the well-known instance of Leopoldia Leopoldina. The presence
of close-set sigmoidal ribs on the upper part of the flanks characterises Hoplite*
cryptoceras, which, according to v. Koenen, has probably its proper place in the
Leopoldina group. 1
It is the suture-line which constitutes the peculiarity of this group. Accord-
ing to the prevailing opinion which is probably correct, the scanty and coarse
ramification of the lobes and their low and broad trunks are to be considered
as a case of reversion. In consequence of the stronger development and higher
position of the outer lateral branch, the first lateral lobe acquires a strikingly
asymmetrical form. D'Orbigny has already correctly represented this form of
lobe in Hoplites Leopoldinus ; latterly the same peculiarities have been commented
upon by Sarasin, A. v. Koenen, and Baumberger. The unsymmetrical configur-
ation of the Leopoldia lobes cannot be connected with that of the lobes of the
amblygonius group. It is true that in the amblygonius group the outer lateral
branch of the first lateral lobe is longer and more copiously ramified than the
inner one ; but it is very narrow, and the whole of the suture-line is copiously
ramified. In Leopoldia, on the other hand, the lateral as well as the terminal
branches are broad, stout and short, and the ramification is of a reduced
type.
This difference in the conformation of the lobes is so considerable that the
possibility of uniting Leopoldia with Neocomites is out of question, at least if
we concede the necessity of subdividing the too comprehensive genus Hoplites
into smaller groups. Solger 2 has already pointed out that the inclusion of the
Leopoldina group in the Upper Cretaceous genus Hoplitides A. v. Koenen is
not a satisfactory mode of procedure. Hoplitides possesses a wide umbilicus;
the external region of its earlier volutions is depressed and accompanied by two
smooth edges and the ribs are more strongly developed on the upper part of
th3 flanks and not, as in Hoplites Leopoldi, on the external margin and the
1 H. cryptoceras has been scleoted by A. Hyatt BB the type of his genus Lyticoceras, to which thit
author refers also H. amblygonivs (~E. noricus). We cannot utilise this name for the Leopoldina group
no more than for the subgenus Neocomites for which it has already been found unsuitable, for Hyatt places
H. amblygonius in the genus Lyticoceras and, therefore, assigns to the latter different limits to those which
we have assigned to it. Moreover, it is by no means certain whether the still insufficiently known species
H. cryptoceras really should be included in this group.
2 Animonitenjavna der Mungokalke und das geologische Alter der letzteren, p. 128.
Jtf!