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

HIMALAYITES. 137
umbilical tubercles as well as prominent external nodes. The ribs are always
sigmoidally curved or deflected forward ; one scarcely ever observes more than two
branch-ribs originating from one and the same tubercle. The whole of these
characters together with the strong ventral furrow impart to Hoplites an aspect
so fundamentally different from that of Himalayites that a separation of Himalayites
from the typical Hoplites becomes unavoidable. The difference between
the two is not only a difference in single, isolated characters, but a difference
in the unpression which each of them produces as a whole.
It is exactly in this respect that the genus Himalayites forcibly recalls
the (weeps-group of Reineckia, more especially Reineckia Brancoi Steinm. and
Reineckia anceps carinata Quenst, The ribs of these ammonites have the same
radial disposition as those of Himalayites; there is a great similarity of form,
size, disposition, and number of tubercles, and, as regards especially the form and
disposition of the bundles of branch-ribs, there is so striking an agreement between
Reineckia and Himalayites that the probability of the existence of a closer relationship
between these two form-groups has to be seriously taken into consideration.
The generic name Reineckia was first introduced by Bayle. 1 Although this
investigator did not furnish a detailed description of the genus, his choice
of types proves clearly that by Reineckia he understood the group of Ammonites
anceps in its wider conception. D. Steinmann was the first who actually established
the genus Reineckia in that sense. 2
Ste inmann' 1 distinguished two main sub-divisions—the series of Reineckia anceps
and that of Reineckia (Jrcppini. In the forms which constitute the latter group
the cross-section of the volutions is already higher than broad at an early stage,
the tubercles approach the umbilical suture, become feebler or may even disappear
ent irely. The forms of this series already acquire during the. middle stages
of development certain characters which fail to suggest a close relationship with
the cycle of Himalayites.
The two species of Reineckia referred to above—R. Brancoi and R. anceps
carinata—which so closely resemble Himalayites, belong to the anceps-group of
Steinmann. Of the members of that group it IB probably only the two just
mentioned by name which possess such a striking resemblance with Himalayites.
The majority of the forms appear to differ appreciably. For instance, intercalary
ribs arc usually entirely absent. The tubcrcles are feebler, more numerous and
placed closer to the .umbilical suture, and the ribs are more delicate. Further
one observes numerous deep constrictions not known to exist in Himalayites, and
the ventral furrow is retained even at the full-grown stage. The sutuie d ffers
1 Explication do In Curtc GAol. do Frnaoc, IV, pi. LVI,
* Stcuer, in his monograph on the Tithoniim of Argentina, has considerably extended tbo confines of
the genua Reineckia by the addition of numerous form*. The forms in question being, however, evidently
of considerable diversity, it sccrrfs advisablo to adhere to the original oonceplion of the genus, at least for
the present. (PoUontol. Abhandlvngen, VII, Heft 3.)
a 2«r Kenntniiw dor Juraformation von Caraoolcs (Bolivia). Ntuea Jahrbueh f. Uineratogie, eto,,
supplementary volumo I (1881), p. 283.