BRITISH FOSSILS. 



DECADE THE SIXTH. 



This the Sixth Decade of representations of British Fossils is 

 devoted to the illustration of some new genera and species of 

 extinct fishes. 



The comparative rarity of these fossils renders it impossible to 

 conform to the plan adopted in the preceding Decades of grouping 

 the subjects either according to natural relations or stratigraphical 

 position. The same cause precludes also the possibility of selecting 

 from the collections of the Geological Survey a sufficient number of 

 novelties to complete a Decade. 



In accordance, nevertheless, with the request of the Director 

 General, that I would undertake the production of an Ichthyological 

 Decade, I have accomplished the task by selecting subjects from my 

 own cabinet and elsewhere, either entirely new, or little known, 

 none of which have hitherto been figured. 



Of these the most interesting is the unique chalk ichthyolite in 

 the collection of the British Museum, described in the last article. 

 The other descriptions comprise a new Palceoniscus, from the coal- 

 measures ; new species of the genera Lepidotus, Pholidophorus, 

 Ptycholepis, and Leptolepis, from the Oxford clay and lias forma- 

 tions ; an Ophiop>sis, from the Purbeck strata, near Tisbury ; and a 

 detailed account of a Chimceroid fish, Elasmodus Hunteri, from the 

 London clay. 



The curious structural details of the latter specimens are beauti- 

 fully delineated in the first copper-plate. The same process of 

 [VI.] b 



