Dr, C. Stnichnann—The Jura of Hanover and England. 555 



a. According to the lists before us the Portland Sand contains 

 only 10 species of fossils, all Conchifera, which are also found in 

 the Hanoverian Upper Jura. Of these only 4 species have hitherto 

 been observed in the Portland formations, namely, Ostrea multifor- 

 mis and Perna Bouchardi, in both divisions, and Trigonia variegata 

 (which, as is well known, is very nearly allied to T. gibbosa) and 

 Pleuromija tellina as yet only in the Plattenkalke. Six species 

 do not occur above the Kimmeridge beds, namely, Ostrea soJitaria, 

 Ostrea Bruntridana, Mytilus jiirensis, Trigonia alina, Lucina fragosa, 

 and Pledomya rugosa. The whole of the 10 species are contained 

 in the Pteroceras-heds. The characteristic fossil of the German 

 and French Lower Portland formations, Ammonites gigas, has not 

 yet been detected in the English Portland Sand ; on the other 

 hand, Ammonites giganteus, Sow., which is characteristic of the 

 Portland Stone, has been determined on the Ith, and also recently 

 by myself on the Deister near Hanover, together with Ammonites 

 gigas, in the Lower Portland. 



b. The English Portland Stone has 23 species of animal fossils 

 in common with the Hanoverian Upper Jura, but the distribution 

 of these within the different zones is very different near Hanover. 

 Only the following 7 species occur in the Portland formations 

 generally: Ostrea multiformis,^^ Perna BoucTiardi,''-' Cyrena rugosa,'^ 

 Pleuromya tellina,^^ Neritoma sinuosa, Ammonites giganteus and 

 Serpula coacervata. Of these the species marked with an asterisk 

 have been observed in the Eimbeckhauser Plattenkalke ; the two 

 others only in the beds with Ammonites gigas. 



Sixteen species, on the other hand, occur only in older deposits than 

 the Portland. Further, it is noteworthy that the Hanoverian Kim- 

 meridge contains all the species in common with the Portland Stone, 

 with the single exception of Ammonites giganteus. Of the 16 species 

 which, according to existing observations, occur only in older beds, 

 the following 13 species have hitherto been found near Hanover, 

 exclusively in the Kimmeridge : — Trigonia Micheloti, Lucina port- 

 landica,'-'' Lucina plebeia, Corbicella Morceana, Soroerbya Dulcei,'-'' 

 Nerita transversa, Natica tiirbiniformis, Notica Marcousana,^' Cerithiim 

 trinodule, Cerithium Boidini, Cerithium Bouchardi, Pteroceras Oceani, 

 and Serpida quinquangidaris. 



With the exception of Lucina plebeia, however, these species have 

 hitherto been found only in the English Portland Stone; those 

 marked with an asterisk are even usually regarded as characteristic 

 of the Upper Portland in England, and this applies also to Cyrena 

 rugosa and Neritoma sinuosa, which in Hanover extend up through 

 the loliole of the Kimmeridge to the Portland. This is the best proof 

 how little dependence is to be placed upon so-called characteristic 

 fossils. To judge correctly of the age of beds, the conditions of 

 stratification are above all things to be kept in mind; then the 

 general character of the fauna is to be estimated, but at the same 

 time the different phases of development in different districts must be 

 taken into account. The small number of the corresponding organic 

 remains in the English and North-German Portland formations. 



