136 
NATJTILOIDEA. 
equivalent to the nodose-keeled species of Trematodiscv^, speak in 
such a convincing manner in favour of the genetic connection be- 
tween the two genera [Trematodiscus and Pleiironautilus] that we 
do not hesitate to place forms with smooth surface and crenulated 
ridges, such as P. gemmatus, in the genus Pleuronautilus. 
“As is indicated in Gyroceras aigoceras, de Koninck (which 
possesses the sculpture of Pleuronautilus)^ it seems quite possible 
that some Pleuronautili have been developed direct from forms 
with open whorls without passing through a Trematodiscus stage . . 
“ The oldest Pleuronautili known to me are found in the Pro- 
ductus-Limestone of the Salt-Range \ and in the Permian-Kalkstein 
of the Araxes Pass in Armenia n 
“ In the Mediterranean Trias Pleuronautilus extends upwards to 
the Middle-Karnischen group ; the genus is, however, wanting in the 
Juvavischen Province.” 
As I consider that the “ Group of Nautilus Trautsclioldi ” of Dr. 
Waagen, already referred to, may be very properly included in the 
present genus, I shall take this opportunity of recapitulating the 
species he comprises in that group, with his remarks thereon, in 
his own words. The first species mentioned by AYaagen is Nautilus 
Trautsclioldi^ N OiOigQTi N. tuberculatus^ Trautschold^, non Sow- 
erby). “ This species was found in the Upper Carboniferous lime- 
stone of Mjatschkowa. To it some forms in the Salt-Range are 
most closely related. They form part of the fauna of the Upper 
Productus-limestone, and I shall describe them under the names of 
Nautilus transitorius, AA^aagen, and N. Wynnei, AVaagenh The 
latter very naturally leads us to Nautilus dorso-armatus, Abich, and 
N tuber cularis, Abich from Djoulfa on the Araxes, and these again 
furnish the connecting link with Nautilus Pichleri, Hauer®, which 
^ Waagen, in Palceont. Indica, ser. xiii. vol. i. 
^ H. Abich, “ Eine Bergkalk-Fauna aus der Araxes-Enge bei Djoulfa in 
Armenien,” in geol. Forschung. in den Kaukasiscben Liindern, Theil i. 1878. 
' ^ ‘’Die Kalkbriiche von Mjatschkowa,” in Nouveaux Memoires de la Soc. 
Impel’, des Naturalistes de Moscou, tom. xiii. livr. i. 1860, p. 302, tab. xxx. 
ff. 3a, Sh. 
^ Mem. Geol. Surv. India — Palgeont. Indica, 1879, ser. xiii. Salt-Range 
Fossils, vol. i. Productus-limestone Fossils. It may be mentioned that Traut- 
scholdi is wrongly spelt Trantscholcli throughout the book. 
° “ Eine Bergkalk-Fauna aus der Araxes-Euge bei Djoulfa in Armenien,” in 
geol. Forschung. in den Kaukasiscben Landern, Theil i. pp. 20, 22, Taf. iii., iv. 
N. dorso-armatus is erroneously named N. tiihercularis on Taf. iv. 
® “ Cephalopoden der unteren Trias der Alpen,” in Sitzungsberichte der k.-k. 
Akad. d. AVissensch. zu Wien, 1865, 621, Taf. i. ff. 1-3. 
