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Mojsisovics to be the same as Acis Afu/ist, 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 Pleuronautilus 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 fur 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 (PL iv, 

 Fig. 3 (?) of my Hallstatter Ceplialopods), referred to Pleuronautilus 

 superbus, cannot be explained as due to compression, but must be 



