54T 
Mojsisovics to be the same as Acés Munst, have been figured on 
Pl. xi, Figs. 4-8, to show that the impressed zone is present only 
after contact in these Triassic species, which have good-sized um- 
bilical perforations and a cylindrical first whorl. 
Pleuronautilus. 
This genus was described by Mojsisovics to include a number of 
costated nautilian shells of the Trias, having in one section of this 
genus shells with the nepionic stage marked by transverse bands 
and in the species copied from Mojsisovics, Pl. xii, Fig. 3, the um- 
bilical perforation is very large. 
In correlation with this the apex is free and the generic char- 
acters appear late in the neanic stage. 
This shell appears at first to be an extraordinary exception to 
the rule that generalized forms, with large umbilical perforations, 
slow growth of the dorso-ventral diameters and more or less cylin- 
drical first volutions, always have a gibbous dorsum in the nepionic 
stage. Mojsisovics’ figure, copied here, Pl. xii, Figs. 4 and 5, and 
in his description, has a dorsal furrow in the paranepionic substage. 
In order to confirm or refute such an important observation I wrote 
a letter of inquiry to Dr. Edmund Mojsisovics von Mojsvar and 
have received in return the following courteous reply, which shows 
clearly that the species cannot be quoted as exceptional in the 
opinion of this eminent authority. I quote below both my trans- 
lation and the original letter : 
‘*Die Impression auf der intern Seite des (auf Taf. iv, Fig. 3, 
meiner Hallstatter Cephalopoden) zu Pélewronautilus superbus 
gestellten Fragmenten kann nicht durch eine Verdriickung 
erklart werden, sondern nun als eine thatsachlich der Schale 
sukommende Eigenschaft betrachtet werden. Ich halte es 
aber jetzt fiir wahrscheinlich, dass dieses Fragment trotz seiner 
grossen Uebereinstimmung mit dem ersten Umgange von Pleuro- 
nautilus superbus nicht zu dieser Art, sondern zu einer andern neuen 
Art gestellt und nicht als erster Umgang betrachtet werden darf. 
Ich neige vielmehr jetzt der Ansicht zu, dass die Impression auf der 
concaven Seite von weggebrochenen innern Umgangen herriihren 
diirfte.”’ 
*‘The impression upon the inner side of the fragment (PI. iv, 
Fig. 3 (?) of my Hallstatter Cephalopods), referred to Pleuronauttlus 
superbus, cannot be explained as due to compression, but must be 
