72 ME. J. W. KIKKBY ON PEEMIAN FISH ANB PLANTS. 



Trias.* On the other hand, they are separated from the Coal- 

 measures by the Middle and Lower Limestones, Marl-slate, and 

 Lower Eed Sandstone, which represent an aggregate thickness of 

 460 feet. Previous to their discovery, the highest authenticated 

 horizon on record for the occurrence of fish in the Permian series 

 of Durham was the inferior beds of the Lower Limestone, f which 

 had yielded a single specimen of Platysomus striatus — the Maii- 

 slate, however, being their chief and almost only horizon. The 

 discovery of the Pulwell fish has, therefore, carried the Permian 

 Vertebrata from the lower beds of the Durham series high into 

 the upper and near enough to the Trias to give to their occur- 

 rence, perhaps, more than usual interest. 



DESCRIPTIONS OP THE SPECIES. 



Class. PISCES. 



Order. GANOIDEI. 



Eam. 1. SAUROIDEI. 



ACROLEPIS, Sp. 



A. Sedgwichii, Ag. Kirkby, Annals of Nat. Hist., 3rd 

 Series, vol. IX, p. 269. 



About a dozen, or probably rather more, specimens of an Acro- 

 lepis have occurred, which may possibly belong to one of the 

 forms of this genus already described from Permian rocks. All 

 the specimens, with one exception, are fragments. The perfect 

 specimen belongs to an individual about ten inches long ; but I 

 possess a fragment that has evidently belonged to an individual 

 of a foot or more in length. 



The maximum height of the ten-inch specimen is between the 

 pectoral and ventral fins, and measures If inch. The head is 



* In some parts of Durham there are more than 200 feet of Permian strata above 

 the Fulwell fish bed, the Upper Limestone being subject to considerable variation in 

 thickness. On the coast of Durham, for instance, between Sunderland and Marsden 

 Bay, the Upper Limestone is over 400 feet in thickness. 



+ I have now a small undesciibed fin-spine of a cartilaginous fish from the Middle 

 Limestone of Tunstall Hill. 



