NAIJTILID^. 
299 
slightly curved towards the umbilicus. The siphon is ventrally 
[dorsally] excentric. The mouth is lunate and narrow. The sur- 
face of the shell appears to have been smooth. Nautilus Bouchard- 
ianus, described and figured by d’Orbigny from the French Gault, 
resembles the Indian species, but is not so globose, and the siphon 
is differently placed.” (Forbes.) 
Remarks. The umbilicus in this species has a somewhat angular 
margin ; the siphuncle is distinctly below the centre. The surface 
of the test, though essentially smooth, is marked with fine lines of 
growth. Describing the difference between the present species and 
N. Bouchardianus, Stoliczka remarks : — “The section [in N. sjohcericus'] 
being usually twice as broad as high, has the greatest thickness at 
about half the height and not near the centre. The umbilicus is 
in itself narrow, but perforated through and has all round a broad 
funnel-shaped depression, on the edge of which the shell attains its 
greatest thickness, and then forms a uniform curve to the other 
side, leaving in this way a very broad outer region. Some speci- 
mens are laterally somewhat flattened, and therefore in section not 
so broad as compared with the height. This flatness is, however, 
perfectly different from that of N. Bouchardianus^ being only strictly 
lateral round the umbilicus to a little distance, and does not in the 
least influence the broadness of the outer region, while in the last- 
quoted species the flatness extends to the outer region and causes 
its [comparative] narrowness. The two species have therefore per- 
fectly distinct characters and may be readily recognized.” 
Horizon. Arialur Group ^ ( = Upper Chalk of England, Senonian 
of France). 
^ This group is the highest of the South Indian Cretaceous series, the name 
being derived from the town of Arialur, in the Trichinopoly district. “ The 
invertebrate fauna of the Arialur group exceeds in richness even that of the 
Utatur beds, no less than 3t)5 species having been detected in the uppermost 
subdivision of the Cretaceous rocks of Southern India. The Cephalopoda 
comprise 36 species, Gasteropoda 138, Lamellibranchiata 117, Brachiopoda 12, 
Bryozoa 23, Echinodermata 26, Anthozoa 10, Foraminifera 1, and Vermes 2. 
It is highly probable that this large number may be due partly to the circum- 
stance that the Arialur deposits comprise two groups differing somewhat in age. 
The lower fossiliferous beds, from which the bulk of the fossils have been pro- 
cured, correspond very fairly with the Senonian beds of France, and the Upper 
Chalk with flints of England. From this horizon all the Cephalopods found 
in the formation have been derived, with the exception of Nautilus Danicus^ 
which was only observed in the upper beds of Ninny ur &c., in the Trichinopoly 
area, although some specimens were obtained, apparently from a lower horizon, 
near Pondicherry.” (‘Manual of the Geology of India,’ by H. B. Medlicott and 
W. T. Blanford, 1879, pt. i. p. 283.) 
