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 
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. 
