OF THE SWISS JT7KA AND ENGLAND. 



263 



The Pterocerian fauna of the northern part of the Jura contains 

 181 species (Greppin, op. cit. p. 110) : 31 of these pass down to the 

 Astartian, 14 also occur in the Virgulian, and 17 are common to the 

 Astartian, Pterocerian, and Virgulian, and there are 6 species which 

 have a somewhat wider range ; this leaves about 120 species peculiar 

 to the Pterocerian. The 181 species include 34 which have been 

 met with in England in the following beds respectively : — 



Lower Oolites 2 



Corallian 8 



Kimeridge Passage-beds and Lower Kimeridge . . 14 



Portland Beds 3 



Hanging from Coral Rag to Kimeridge Passage- 

 beds 5 



Ranging from Upper Calcareous Grit to Portland 



Beds 2 



34 



The 14 Kimeridge-Clay species include 6 which pass up from the 

 Astartian ; the following are the remaining 8 species : — 



Ammonites rotundatus, Sow. *Trigonia muricata, Goldf. 

 Neritopsis delphinula, J)' Orb. *Astarte pesolina, Contj. 

 Pholadomya acuticosta, Sow. Cardium pseudoaxinus, Thurm. 

 Protei, Ag. Ostrea Bruntrutana, Thurm. 



The two species marked * are also recorded from the Virgulian. 

 The commonest and most characteristic fossil of this stage (Pteroceras 

 ocertni) has not, as yet, been found in England. The Abbotsbury 

 Ironstone has yielded a species of Pteroceras (Q,. J. G. S. vol. xxxiii. 

 p. 274) ; this deposit is, as already stated, included in Blake's Kim- 

 eridge Passage-beds, and is too low in the series to be correlated 

 with the Pterocerian. No* true Pterocerian fauna is known to occur 

 in England, though, as Blake points out (Q. J. G. S. vol. xxxi. 

 p. 215), " several of the less peculiar fossils of that group are found 

 associated with Lower Kimeridge forms," a statement which fully 

 agrees with the conclusions to be derived from the fossils quoted 

 above. In the absence of a Pterocerian fauna in England, it is 

 of course difficult to find their equivalents in this country ; what 

 evidence there is clearly points to some portion of the Lower Kim- 

 eridge of England as being the representative of the Pterocerian 

 of the Jura. Blake, in referring to the Pterocerian of the Paris 

 basin, states that the stage " is adopted solely in deference to its 

 probable justification in the area where it was first introduced, 

 namely the Jura, and to its distinctness paleeontologically when the 

 fossils of any locality have been studied. Neither in the basin of 

 Paris, nor in any other part yet studied, is it sufficiently distinct to 

 be of much importance in the field " (Q. J. G. S. vol. xxxvii. p. 578). 

 It has already been shown that in the Jura the Pterocerian fauna is 

 very well marked, and it would appear that it diminishes in impor- 

 tance in a north-westerly direction, and disappears altogether before 

 reaching England. 



