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

HOPLITES. Jtf!
especially when W. Kilian was able to correctly point out the close rekuiorwhip
of the amblygonius group with Hoplites neocomiensis.
Indeed, there exists no essential difference as regards the shape and orna-
mentation of the shell between Hoplites neocomiensis and Hoplites amblygrmius.
It is only the suture-line which reveals any difference, the first lateral lobe of
Hoplites neocomiensis being sub-symmetrically developed, with a uniformly broad
trunk, nearly equally strong lateral branches and a terminal branch which is a
direct continuation of the trunk, while the first lateral lobe of Hoplites amJAy-
gohius exhibits the asymmetrical structure already described.
Nothwithstanding the close relationship between Hoplites neocomiensis and
Hoplites amblygonius the type of suture characterising the North German forma
has not, so far as we know, been discovered in any of the Alpine species of AV>-
comites and vice versa. This statement has been confirmed lately by the ex-
perience gained in Northern Germany as well as in the Carpathian region of
Silesia. All the forms of Neocomites which have been described in the year
1901 from the Upper Teschener Slates of Silesia, which belong to the Alpine
Province, exhibit, without exception, the Alpine type of lobes, whilst the North-
ern German forms of Hoplites with which v. Koenen acquainted us are as con-
sistently characterised by the Northern European type. 1 We have, therefore,
to reckon not only with the really existing relationship of the amblygonius group
with Hoplites neocomiensis, but also with the divergence in the development
of the lobes in the Alpine and Extra-Alpine regions of Europe. The recent
advance in our knowledge has not altered any of the notions previously acquired:
the amblygonius group remains restricted to the Northern European province,
and the proof of a close relationship with Neocomites neocomiensis does not in
any sense detract from its palaeogeographical significance. It only remains to
consider what is the most convenient way of emphasizing this fact in the classi-
ficatory system.
It is impossible to look at the divergent structure of the lobes of the group
under discussion in the fight of a variation in the ordinary sense of the term,
for the divergence does not affect single individuals found in the same locality,
but is characteristic of extensive groups belonging to distinct provinces.
Neither have we to deal here with provincially vicarious variations, for we have
also to reckon with a difference in the geological age which, although small,
is by no means negligible, in so far as the group of Neocomites neocomiensis
has its home in the Valanginian, whilst the group of Hoplites amblygonius be-
longs to the Lowest Hauterivian. It would be contrary, therefore, to the evidence
of established facts to represent Hoplites amblygonius as a variety of Neocomites
neocomiensis, and we cannot but adhere to our previous decision in regarding
l Even the North German form which was designated as H. neocomiensis d'Orb. (?) by v. Kooxn haa
an asymmetrical first lateral lobe ; it differs, therefore, from H. neocomiensis in an ioiportaot pokit, and foe
this reason cannot be identified with the later species. This appearB to have been felt by A. T. Koeam, AA
-undisputed authority on the Neooomian of Germany, as is shown by the query.