264 



ME. T. ROBERTS ON THE UPPER JURASSIC ROCES 



The Pterocerian fauna of the southern district of the Jura is 

 poorer in species than that of the northern, since it numbers only 63 

 species (Jaccard, op. cit. p. 193), 17 of which occur in England (9 in 

 the Corallian, 4 in the Lower Kimeridge, 1 in Upper Kimeridge, and 

 3 range from Corallian to Lower Kimeridge). Exogyra virgula* is 

 recorded from these beds, but apparently does not occur in any 

 abundance. They may, however, represent a portion of the Yir- 

 gulian of the northern district, which has not been recognized as a 

 distinct formation in the central J ura. 



Greppin (op. cit. p. 118) records 118 species from the Yirgulian 

 of the Jura Bernois, and this includes 21 British species, of which 

 1 occurs in the Lower Oolites, 6 in the Kimeridge Passage-beds 

 and Lower Kimeridge, 1 in the Upper Kimeridge, 3 in the Port- 

 land Beds, while 7 range from the Corallian to the Lower Kimeridge, 

 and 3 from the Corallian and Lower Kimeridge to the Portland 

 beds. The Lower-Kimeridge forms are : — 



Ammonites longispinus, Sovj. 

 Anatina parvula, Et. 

 Area sublata, D' Orb. 



Astarte pesoliua, Contj. 

 Lima virgultna, Contj. 

 Exogyra virgula, Desm. 



Pour of these fossils are peculiar to the Yirgulian of the Jura. 

 The upper beds of the Lower Kimeridge Clay of Cambridgeshire are 

 crowded with Exogyra virgula (Sedgwick Essay for 1886, MS.), 

 in fact one bed is for the most part made up of the shells of this 

 small oyster. Precisely the same thing occurs in these beds in the 

 Jura, the only difference being that in the last-named locality the 

 matrix in which the fossils are imbedded is slightly more calcareous 

 than the zone in England. Ammonites longispinus is associated 

 with Ex. virgula in the upper portion of the Lower Kimeridge 

 of Cambridgeshire. Elsewhere in England Ex. virgula has been 

 commonly met with in the Lower Kimeridge, and extends into the 

 lower part of the Upper Kimeridge ; it is, however, more character- 

 istic of the former subdivision. The palseontological evidence 

 therefore points to the upper division of the Lower Kimeridge Clay 

 of England as being the equivalent of the Yirgulian of the Jura : the 

 latter should certainly be placed on the horizon of the virgula-hed at 

 Ely, and probably also on that of the zone of Amm. alternans which 

 underlies this. Blake correlates the Yirgulian of Prance with that 

 portion of the Lower Kimeridge which overlies the zone of Ostrea 

 deltoiclea &c. ; but we have seen reason to believe that a part of this 

 is on the horizon of the Astartian of the Jura. 



The Portlandian of the Jura, although of considerable thickness, 

 contains but a poor fauna. Jaccard (op. cit. p. 187) records 47 spe- 

 cies, and Greppin (op. cit. p. 123) 35 species from this stage ; deduct- 

 ing 8 species common to both lists, this gives a total of 74 species 

 from the two districts. Amongst these there are no less than 



* Oppel (op. cit. p. 751), apparently referring to the Pterocerian of the Bernois 

 district, mentions the occurrence of a solitary specimen of Exogyra virgula from 

 this stage. 



