PREFACE. XIX 



here likewise the type is exchanged for one of subordinate 

 size in the case of two families (Phasianidce and Siluridce), 

 one containing no true natives, the other only a doubtful 

 native. In accordance, also, with the rule before given, 

 the former is distinguished by an asterisk ; the latter, by 

 the name standing in ITALIC CAPITALS, and its being, 

 as in the case of sub-genera similarly circumstanced, without 

 a number. 



The specific characters, which are for the most part 

 entirely new, have been drawn up, as far as practicable, 

 with a view to the exact differences of species ; but the 

 difficulty of doing this in the instance of the aquatic Birds, 

 which are subject to such great changes of plumage from 

 age and other circumstances, it must be confessed is very 

 great, and has not in all cases been satisfactorily got over. 

 In the Class of Fish, specific characters have seldom been 

 added in the case of genera or sub-genera containing not 

 more than one British species, or when given, bear refer- 

 ence solely to other, nearly allied, European species ; the 

 essential characters of those met with in other countries, 

 in many groups, not having been hitherto determined with 

 precision. 



The terms employed in characterizing the larger groups, 

 or in drawing up the descriptions of species, have for the 

 most part been derived from the works of Illiger*, Des- 

 marest -j-, and Cuvier. The " Histoire Naturelle des Pois- 

 sons" of this last author has been exclusively resorted 

 to in the Class of Fish. To these works, the reader, to 

 whom the terms are not familiar, is accordingly referred. 



* Prodromus Systematis Mammalium et Avium. Berol. 1811. 8vo. This 

 work will be found to contain a very complete terminology with reference to 

 the two classes of Mammalia and Birds. 



-j- Terminologic des Mammiferis ; prefixed to his " Mammalogie." 



