112 
Records of ihe Geuloy ical Survey of India. 
[voL. xiir. 
T. glVlosum is moderately involute, leaving a wide and shallow umbilicus ; 
the shell is thickest, near the middle of the sides, in the region of the “bumps,” 
which occupy exactly the centre-line of the sides, and are about six in number 
in the last whorl. The inner whorls are quite smooth, and on the surface of 
the shell itself neither ribs nor strife arc visible. The section of the mouth 
is oval, widest about halfway up the sides. The siphonal, side is perfectly 
rounded. The body-chamber, as far as it is preserved, amounts to about half a 
whorl (the arrow indicates the commencement of it, fig. 10). 
The lobes are very simple and resemble those of OpMceras medium, n. sp.> 
and partly also those of Traoh, semipa^-titum, v. Buch. Besides the low siphonal 
lobe there are one external and two lateral lobes with one auxiliary lobe, which 
is situated near the umbilical margin. The antisiphonal lobe is deep and ends 
in two minute points (fig. lOi). 
Tribe: AEGOCERATID^, Waag. 
Genus: XENODISCUS, Waag. 
Xlixoniscus DKMISSUS, 0pp. 
1862. Ammonites demissns, 0pp.: Pal. Mitlb., Taf. 86, fig. 1. 
1872. Ceratites carhonarhts, Waag.: Mem. Gcol. Surv., India, Vol. IX, PI. I, figs, 2 & 3, 
1879. Xenodiscus carlonarius, Waag.; Palmont. Ind., Sor. XIII, PI. II, figs. 2 to 5. 
With the species above described and in the same bed (2) with Posidonomya 
angusta, Hau., and other Werfen bed fossils, occur numerous specimens belonging 
to a chain of forms which might bo roughly described as beginning with the 
Hat and characteristic Xenodiscus demissus, 0pp., and ending with Xenodiscus (?) 
hucliimms, DeKon. 
I have nothing to add to the description of the above-named species after 
tlic excellent exposition given by Waagen in tho Pala3ontologia Indica, but may 
add, that there can be no doubt that OppeTs figure agrees with Waagon’s species, 
as it does with my specimens. Tho species is so common in bed 2, that 
necessarily there is a great variety of forms, all, however, agreeing in the 
ju'incipal characters. They show greatest xairiation in the ribs or wrinkles of 
the shell, to which I may add that the shell itself is rather thick, especially so 
lialf-way up the flattened sides, and is covered by wrinkly linos of growth, which 
at intervals developo into ribs. 
It is poSiSiblo to arrange from amongst them a complete chain, passing from 
the evolute specimens (representing Oppel and Waagen’s species) uj") to consider¬ 
ably involute varieties, and in that stage closely resembling tho two species of 
DoKonirick’s GonintHes gangeticiis and Ger. buehimms. 
Though Dr. Waagen does not say so in his description of the new genus, 
1 presume that Xenodiscus is really the early stage of development of Aegoceras, 
Waag., and stands in the same relation to the latter genus as ilocs Otoceras and 
Ophiceras, I’cspoctivcly, to Finacoceras and Lytoceras. 
