CEPHALOPODA OF THE ZLAMBACH AND HALLSTATT BEDS. 7 



11. The Cephalopoda of the Zlambach and Hallstatt Beds. 

 By Dr. E. von Mojsisovics. 



[Proc. Imp. Geol. Inst. Vienna, June 17, 1873.] 

 Dr. von Mojsisovics has published, as the first number of the sixth 

 volume of the ' Abhandlungen ' of the Imperial Geological Insti- 

 tute of Austria, the first part of his geological investigation of the 

 neighbourhood of Hallstatt, in which he describes the remains of 

 Cephalopoda obtained from the Zlambach and Hallstatt beds. These 

 are numerous, and belong to the following genera : — Orthoceras 

 (9 sp.), Nautilus (38 sp.), Lytoceras (14 sp.), Phylloceras (6 sp.), 

 Pinacoceras, g. n. (32 sp.), Sageceras, g. n. (1 sp.), and Arcestes 

 (16 sp. belonging to the group of A. tornatus). 



"With regard to Orthoceras, the latest representatives of which 

 occur in the Upper Trias, the author states that in all the species 

 with a long body-chamber the occurrence of the peculiar impres- 

 sions of the adherent surface of the mantle (stries creuses of Bar- 

 rande), first observed by the brothers Sandberger, was ascertained; 

 and in a species with a short body- chamber, distant septa, and nar- 

 row siphuncle, the occurrence of a periodical truncation associated 

 with a formation of terminal caps seemed to be very probable. 



In his treatment of the Ammonites the author adopts the classifi- 

 cation inaugurated by Suess, and carried out for the Jurassic Am- 

 monites by Waagen and Zittel, regarding the course adopted by 

 these authors as the only one likely to lead to a natural (or genea- 

 logical) view of this group of fossils. He indicates repeatedly, espe- 

 cially in connexion with the genera Lytoceras, Pinacoceras, Sage- 

 ceras, and Arcestes, that he can by no means arrange the Goniatites 

 as a distinct generic series in opposition to the Ammonites, in ac- 

 cordance with the views of L. von Buch, Beyrich, and Giebel. The 

 Triassic representatives of the above-mentioned genera are most 

 closely related in all essential peculiarities of organization and habit 

 to Goniatitic predecessors ; the Ammonites from the Permian sand- 

 stone of Artinsk, Waagen's Permian Ammonite from the Salt range 

 of the Punjab, and] certain Triassic forms partially bridge over the 

 gap which still exists between the older Goniatites and the Ammo- 

 nites of the Trias. By far the greater part of the genera of Am- 

 monites occurring in the Alpine Trias have their roots in the Palae- 

 ozoic Goniatites ; and some of them may apparently even be traced 

 back into the Upper Silurian formations. The greater part of these 

 Palaeozoic genera become extinct in the Upper Trias, when they at- 

 tain the height of their development, but at the same time show 

 signs of senile degradation, analogous to the phenomena observed 

 during the gradual extinction of the later Ammonitic types in the 

 Cretaceous period. 



The character of the Ammonite-fauna of the upper Alpine Trias 

 is preponderantly Palaeozoic, in striking contrast to that of the beds 

 with Arcestes Studeri, in which JEgoceras and Amaltheus, which are 

 wanting in the faunas of Hallstatt and St. Cassian, have already 

 made their appearance. Of the later genera only Phylloceras and 

 Lytoceras are represented by a few forms. 



