546 PROF. PAVLOW ON THE CLASSIFICATION OF THE [Aug. 1 896, 



of the so-called Volgian stages, shows clearly the Jurassic age of 

 both of these stages, and cuts the ground from under the feet of the 

 defenders of the Cretaceous age of one or both of these stages. 



This bed, with Hoplites of the riasanensis-gronp, thus capping 

 the Upper Jurassic Series, passes upwards in its turn into a 

 glauconitic sandstone with the fauna of the lower zone of the 

 Petchorian, that is to say, of the boreal Lower Neocomian series. 

 The Hoplites of the riasanensis-grou-p, though rare, continue to be 

 met with in this bed, which contains also a great number of Aucellce 

 (especially A. volgensis) and Belemnites of the lateralis- and sub- 

 quadratus-gr oups. This bed is, in turn, capped by sands containing 

 rough sandy phosphorites with Olcostephanus hoplitoides, representing 

 the upper zone of the Petchorian Series, that is, the zone of Poly- 

 ptychites polyptychus and Keyserlingi, and we find there many forms 

 common to the corresponding horizon of Syzran and of the Petchora 

 region. The fauna of this second horizon of the Petchorian is very 

 rich and varied. Its most characteristic fossils are ammonites of 

 the group Polyptychites, belemnites of the lateralis and subquad- 

 ratus groups, and some species of Trigonia. Aucellce are very rare 

 in this zone in the government of Riasan. Recently I have found 

 in it a fragment of Hoplites neocomiensis, which facilitates the corre- 

 lation of the zone, and of the whole Petchorian, with the corre- 

 sponding zones of the Lower Neocomian of Western Europe. 



Thus we have in Russia a well-developed ' Aquilonian ' stage, 

 corresponding to the Purbeck, and an equally well-developed 'Lower 

 Neocomian,' having many species in common with the West European 

 Lower Neocomian but bearing a special stamp, expressed in the 

 presence of fossils of boreal type, especially of many species of 

 Aucellce (partly undescribed) and of belemnites of the subquadratus 

 and /agrafe-groups. This boreal Lower Neocomian (Petchorian 

 Series) bears a close faunistic relation to the underlying Jurassic 

 rocks of the Aquilonian stage, and is in Russia marked off by a 

 well-defined break from the Upper Neocomian (beds of Simbirsk), the 

 intermediate beds of Speeton with Hoplites regalis being here absent. 



The Russian Lower Neocomian is, moreover, subdivided into 

 two zones : (1) The lower zone of Olcostephanus stenomphalus, 

 corresponding to the zone of Ammonites Marcousanus, and indeed 

 containing rare representatives of this species; and (2) The upper 

 zone of Polyptychites polyptychus and Keyserlingi, corresponding 

 to the zone of Hoplites neocomiensis and containing very rare repre- 

 sentatives of this species. 



The Aquilonian stage, which is the marine equivalent of the 

 Purbeck, is also subdivided into the following zones (from below) : 

 (1) zone of Ammonites fragilis, subditus, and catenulatus ; (2) zone 

 of A. nodiger and subclypeiformis ; (3) zone of Hoplites riasanensis. 

 All these zones are so related to each other by the presence of the 

 same Belemnites and Aucellce as to form a natural group, corre- 

 sponding to the Purbeck and to the Upper Tithonic, and containing 

 in the uppermost zone forms with Neocomian affinities. 



