ialontolngia ndita,

1.78
REVISION OF THE JURASSIC CEPHALOPOD
the figure alone, but it had been included by Lemoine in the synonymy of
his 'local race ' 'M'. rnadagascariensis," discussed below. The third of Waagen's
types, the suture-line of which was figured (pl. XXXIII, fig. 5), has very
slightly coarser costation than the other specimens so far mentioned, but there
are various additional examples that · show slight individual differences, also
transitions to the more extreme M.· chariensis.' Those ho have studied large
numbers of Macrocephalites will know that as in most other ornamented ammonites
there are so many differences in ribbing as well as in whorl-shape and
coiling that no two examples are identical.
In some of the specimens there is an attempt at repeated peripheral furcation
of the ribs as in the form referred by G. Boehm (1912a, p. 162, textfig.
72) as a variety gamma to his far too comprehensive 'Macrocephalites
keeuwensis '. This is also seen in some examples of M. madagascariensis and
even lndocephalites ransitorius (pl. XXIII, fig. ·2a), but these forms have distinct
primary ribs. One specimen with very small umbilicus and finer costation
converges somewhat towards the species here described as M. triangularis·
Apparently the earlier forms (e.g. Jumara examples from the lowest flags immediately
above the Patcham limestone), although unfortunately crushed, have
either a smaller umbilicus or else finer costation. than the later typical Golde
Oolite examples, or they converge towards M. trigonalis or M. chariensis in
whorl-section.
The fragmentary Northampton specimen (B. M. No. C 82389) previously
referred to as the only British specimen showing some resemblance to the
forms of the formosus group, is less close to Sowerby's species than to M.
madagascariensis, referred to below, with distinct primary ribs ; but Blake's
large Garsdon specimen, figured (m part) as M. 'compressus ' (1905, p. 45,
pl. IV, fig. 4)1, like other true M. macrocephalus from Wurtemberg (e.g. B.
M. No. C 1141, 50452, etc.) in their smooth outer whorls show resemblance to
the adult M. formosus.
A Khera fragment shows the massive cast of the siphuncu1ar tube, 2-3 mm.
in thickness at a whorl-height of 70 mm., and constricted at the apex of the
median saddle in the external lobe.
jlfacrocephalites dicosmus Gemmellaro sp. {1872, p. 22, pl. II, fig. 5. , in
side-view, seems indistingmshable from Waagen' figure body-chamber example
and the differences in the proportions of whorl-height (47 per cent. instead of
50 per cent.) and .umbilicus (16 per cent. instead of 14 per cent.) are not of
importance. The body-9hamber, . however, is probably similar in most true
Jllacrocephalites. The apparently closely allied M. mantararanus, G. Boehm
(1912, p. 159, pi. XXXV, figs. 3a, b; text-figs. 68a, b, p. 160) has a more
compressed whorl-.section and a more elaborate suture-line.
Horizon :-Lower Callovian, [triangularis 1] dimerus and diadematus zones.
Localities :-Waagen's localities include Surka, Jumara, Khera, and Juria,
all in the median of the three great Kachh ranges. Whether his examples
. a Associ&ted with a. gigantic M. rohmd'IUI, Queuatedt (1887, pL LXXVI, fig. ll), rongly compared by Hlak with
Kamptokephalt!ell terebralu,.y (Phillips).