DE VERNEUIL AND d'aRCHIAC ON RUSSIAN PALJEOZOIC FOSSILS. Ill 



voniati limestones of the banks of the Rhine. The Cyrtoceratites 

 are also represented by three species, all of them new ; one of the 

 most interesting is C. Archiaci, which seems to have a bead-like 

 siphuncle like certain Orthoceratites of the group of Cochleati. 



Contemporaneous with the Orthoceratites in their first introduc- 

 tion, the genus Lituites was still more limited in point of distribu- 

 tion in time, and its existence does not seem to extend beyond the 

 Silurian rocks. The four species that we have seen in Russia be- 

 long to the lower members of the series, three of them occur in beds 

 of the same age in Scandinavia and England, and one of the three, 

 L. cornu-arietis, even extends as far as America. 



The genus Nautilus is less ancient than Lituites, and with the ex- 

 ception of two species in the isle of Odinsholm mentioned by M. 

 Eichwald, no species appears in Russia in rocks older than the car- 

 boniferous period, a fact however which is little in accordance with 

 the observations made in other countries. The species thus found 

 are also for the most part of small dimensions, and affect that discoid 

 flattened form with a large umbilicus and open whorls which re- 

 markably distinguishes the Palaeozoic from the Secondary species of 

 this genus. They are also carinated, or provided with one or more 

 ridges on the back of the shell, — another mark peculiar to the Nau- 

 tili of this period. The local conditions seem to have been little 

 fiivourable for their development in Russia, for not only is the num- 

 ber of species so limited that there have hitherto been only six de- 

 scribed — less than a fourth part of those discovered in other coun- 

 tries — but their distribution is inconsiderable and altogether local. 

 N, tuherculatus is the only one that we have found in several loca- 

 lities, four others are limited to the Ural, and the sixth is peculiar 

 to the Donetz. Of our six species, three are new, and three known 

 in other countries. 



The genus Clymenia, generally characteristic of Devonian lime- 

 stones, is altogether absent in Russia, but according to M. Eichwald, 

 two species have been found in the Silurian beds of the isle of Dago, 

 and one in that of Odinsholm. We have however some doubt with 

 regard to this, for the specimens so described and shown to us by 

 M. Eichwald do not exhibit the angular septa of Clymenia, and 

 some of them must probably be re-united to Lituite or Nautilus. 

 According to M. Pusch, one of the most common of the Fichtelge- 

 birge species occurs at Kielce in Poland. 



Considered vvitli reference to the period of their introduction and 

 extinction, the Russian Go7iiatites ibllow the usual law as observed 

 in other parts of Europe, being extremely rare in the Silurian rocks, 

 where they have only been observed by M. Eichwald, being deve- 

 loped in the Devonian and carboniferous scries, and then disappear- 

 ing. They combine with a rather remarkable local development a 

 very limited distribution, the eighteen species which have been de- 

 termined being derived from only three localities. The species 

 from Artinsk are the most interesting, their lobes being often sub- 

 divided in a manner, the form of which reminds us of that of the 

 lobes of Ceratites and Ammonites, without however indicating a 



