252 OUR COMMON BRITISH FOSSILS. 



near Tynemouth, where nests of minute Rissoa-like 

 univalves are found. Bakevellia and Schizodus are 

 the characteristic bivalves. The former used to be 

 met with in great abundance in the Permian marls 

 at Collyhurst, Manchester, but the place is now com- 

 pletely built over. The best Permian fossil-bearing 

 localities are in Durham. About one-half of the 

 fossil animals found in the Permian strata of Great 

 Britain are mollusca, which fact is a fair index to 

 the comparatively rapid manner this group had deve- 

 loped since its first scanty representation in the Cam- 

 brian formation. Some important genera first appear 

 in the Permian, most notable among which, perhaps, 

 is the genus Mytilus, or the true mussel family. 



