INTRODUCTION. xi 



history but imperfectly ascertained, but in the case of common 

 •species this unsatisfactory nature of the literature is unjustifiable. 

 It is, however, a matter of sincere gratification to find that the 

 important want complained of is to a great extent supplied, and 

 that a systematic arrangement of the subject-matter is adopted in 

 Dr. Day's new work, one which is destined to be of great service 

 to the British Ichthyologist. 



The Faunistic Position of Species. — The most impor- 

 tant requirements in the compilation of a local fauna are a careful 

 definition of the true faunistic position occupied by each species, 

 and of its distribution and relative numbers within the area 

 treated of, together with some notice of its migratory movements. 

 To these should be added — in the case of the rare species — lists 

 of all the occurrences, with dates, localities, authorities, and such 

 other details as are likely to be of service. 



For the purpose of defining the faunistic position of the York- 

 shire Vertebrata the following terms are employed : — 



Residents . . . ) . ^ 



„ ,, [ = Annual Breeders. 



Summer Visitants . \ J 



Winter Visitants . " = Regular Visitors. 

 Periodical Visitants ., 



Casual Visitants . .) , ,^ 



[ = Irregular Visitors. 

 Accidental Visitants) 



These terms are more easily applicable to the birds than to other 

 classes of the vertebrata, from the greater facility with which 

 their movements can be observed and noted. In the case of the 

 marine fishes and cetaceans the terms would be quite as appro- 

 priate, were it not for the veil of obscurity which invests their 

 habits, and in a lesser degree the small attention which they 

 receive at the hands of local naturalists. Owing to this considera- 

 tion, it is advisable in defining — and more especially in illustrating 

 — the terms, to speak of them as applied to birds. 



