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

HOPLITES. Jtf!
Storesi Stanton HopUtes angulatus Stanton, and HoplUes crassiplicMus buntoa
belong also to Thurnumnw (Bull. U.S. Geol. Survey, l33)
W. Kilian 1 was the first to lay special Rtri>n» L iv. ' i x • ,
ni ffnml'iioo ti xj , 1 ess 011 the characteristic features
of ffo^es 2 ««»»,. He showed that in ffopKtea 8imi]arly
neocomiensis and HopUtes amblygonius, there appear bundles of ribs
which become branched on the flanks; whilst, however, the branching of the ribs
of HopUtes amblygonius and HopUtes neocomiensis takes place at various heights
T h o Z I ' i 7 r^ m i ddle ° f ^ flaUkB ' ^ ^nching-pomtsof theTb
flLkl Thurmmni he UmfOTm] y at the same height above the middle of the
The situation of the branching-points of the ribs at the same height above
the middle of the flanks, is not only characteristic for HopUtes Thurtmnni, but
also for the remainder of the forms grouped under Thurrmnnia, and together
with other characters secures to this group a certain degree of independence.
On the flanks the ribs are slightly sigmoidal, almost after the manner of those
of Perisphinctes, and only in the vicinity of the ventral face do they exhibit
a slight forward curvature. In the ear Her and middle stages of growth the ribs
are interrupted on the external margin, but the rib-terminations are only slightly
thickened and distinctly transverse. In the full-grown stage the external region
becomes rounded and the ribs traverse it uninterruptedly with only a slight
reduction. In certain forms, the number of single ribs is greater than that of
the bundles of ribs. Single ribs appear to be especially numerous on the inner
volutions; the sculpture then shows a considerable resemblance to that of Berria-
sella and to that of the non-tuberculate primitive stage of certain forms of Acan-
thodiscus, such as Acanthodiscus Michaelis Uhlig. This resemblance becomes
accentuated by a tendency towards a thickening of the points of origin of the
bundles of ribs on the umbilical wall and at the upper branching-points.
The suture-line is not known in any case: according to Kilian that of
Hoplites Thurmanni approaches that of Hoplites pexiptychus and Hoplites neo-
comiensis.
The subgenus Thurmannia is certainly not so satisfactorily characterised and
sharply defined as the subgenus Kilianella. Nevertheless we have to concede
to it a certain degree of independence. The costation is of a more primitive
character than that of Hoplites neocomiensis and Hopl. amblygonius, and notwith-
standing a certain general resemblance it cannot be placed on a level with the
species just mentioned. With regard to the costation, there is a somewhat
greater resemblance to Hoplites Theodorii Oppel in so far as in the latter
species frequent single ribs also make their appearance and their shape is
slightly sigmoidal and perisphinctoid on the flanks. But the ribs of Hoplites
Theodorii and its nearest allies are deeply cleft, constituting a feature connected
with a somewhat different type of costation.
1 Sur quelques C&phalopodes novveauz on peu connw. Grenoble 1802, p. 10.