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

HOPLITES.
secondary ribs disposed in bundles of three to HI*. Blanf. Urtvb/ma »oA
Blanf. Cricki constitute somewhat of a transition between the third and fint
groups.
The third group is especially of morphological interest. Here we meet
forms such as Blanf. Celebrant and Blanf. Middlemissi in which the characterwtk
mutational tendency has been carried to such extreme limitB that they hare
developed into types which have an entirely foreign aspect and, instead of
presenting the characteristic features of Hoplites, rather recall certain form* of
Holcostephanus, of Perisphinctes (especially Perisphinctes Pottingeri Waagen and
Futterer) or of Himalayites or certain Reineckias. Indeed, it requires Bone care
not to overlook the connection of these extreme types with the more primitive
forms. Certain branches of the Holcostephanus stock acquire a certain degree of
resemblance to Blanfordia: thus amongst the species of Sjnticeras we notice
especially Spiticeras Stanleyi Opp. sp. (pi. XVI), among6t those of J >olyptichest
Polypt. K&yserlingi Neumayr et Uhlig, Polypt. marginatus Roemer, Polypi, polyptychus
Keys., while amongst Simbirskites, there is Simb. coronula Koenen. Although
Himalayites differs by its long intermediate ribs which reach down to the
umbilicus, its resemblance to the extreme forms of Blanfordia may become exceedingly
close, as is also the case with Reineckia, especially Reineckia Uuior
Steuer. We have here to deal with an instructive instance of the convergence
of several branches of Ammonoids, the starting points of which are certainly
located at considerable distances from each other.
Much more formidable than these cases of convergence are the difficulties
encountered in the attempt to elucidate the relation of the Asiatic genus Blanfordia
to the genus Berriasella, as previously defined. Berriasella as compared
with Blanfordia, consists of forms of smaller growth, with finer and more numerous
ribs, steeper umbilical walls and less ramified lobes. Moreover, the ribs
of Befria&ella are somewhat less sigmoidally curved and here and there exhibit
a tendency to become thicker at their points of origin, whilst the ribs of Blanfordia
are very inconspicuous at their umbilical origin and increase in thickness
up to the middle of the flanks.
These differences would hardly deserve beiDg noticed, were it not for the
fact that Blanfordia constitutes an exceedingly homogeneous group, whose evolution
proceeds along lines not at all noticeable in Berriasella. Those strongly
divergent forms with inflated volutions, thickened tuberculiferous main-ribs and
numerous secondary ribs which stamp the Asiatic section of Blanfordia as so
characteristically distinct, are entirely wanting within the form-circle of Berriasella.
In any case the fact that Blanfordia is related to Berriasella cannot be
established without a certain amount of detailed investigation. On the other
hand, the generic identity of the British Indian species of Blanfordia with those
from the Dutch East Indies is evident at first sight.. This fact appears to be of
the greatest possible significance in connection with the direction in which the
development of Blanfordia has proceeded and speaks strongly in favour of the
-unity and well-defined position of the group besides assisting us to fonn a
MA