* Dr. Fleming has alluded briefly to several other species which have been included by some authors in the British Fauna, but the claims of these to be considered as true natives being extremely doubtful, they are not here taken into the account.
A few remarks may now be made upon the particular plan which is adopted in the present work. And first, it must be stated why a deviation has been made from Dr. Fleming's method of separating from the other species, and partially excluding from the British Fauna, those animals which have occurred as Stragglers only in a few rare instances. The reason is founded in the impossibility of drawing any marked line where such separation shall commence. However just it may be in general terms to speak of the animals of any country under the three heads of Residents, Periodical Visitants, and Irregular Visitants or Stragglers, it must be obvious to every one that between the last two there exists so little boundary, that there are many species of which it is difficult to say whether they belong to the former, or to the latter of these divisions*. Every intermediate degree of frequency, as regards the visits of different species of Birds to this country, may be found between what constitutes an annual migration and a solitary appearance. There are some which occur most years in greater or less numbers, though not with that unerring punctuality which attends the movements of our more regular migrants; there are others which only shew themselves at uncertain and more distant intervals; there are others, again, which have not been observed in more than a few instances; and of these last a series might easily be made out in which such instances became continually fewer, till the number was reduced ultimately to one. Now under such circumstances it is clearly impossible to draw the line which Dr. Fleming has attempted to point out. For this reason, in the present work, the species above alluded to are noticed exactly in the same manner as those which are permanently resident in this country, or which visit it at fixed intervals. In so doing there is no wish to raise them to a higher rank in the Fauna than they really deserve. They are still considered only as Stragglers to a greater or less extent. But if it be the object of a Fauna to present naturalists with an account of such animals as are to be met with in their own country, it must surely include all those which have been known to occur in it hitherto. Neither is the reason obvious why the characters, or even a detailed description, of such species, should be suppressed. If it be quite certain that they have appeared in one instance, it cannot be deemed improbable, clearly not impossible, that they may occur in other instances*, and should this prove to be the case, it is very desirable that the student should have the means of identifying them.
* The exact number of species given by Mr. Selby is two hundred and eighty-«even, but six, if not seven, of these cannot be considered otherwise than as doubtful natives.
* Dr. Fleming himself must have experienced some difficulty in determining what species were to be "degraded to the rank of Stragglers," judging from the circumstance, that some which he has only briefly noticed as of this character, have in fact occurred in this country oftener than, many quite as often as, others described at length in the body of his work.
A line of quite as much importance, in the opinion of the author, as that on which Dr. Fleming has insisted, and one more easily drawn, though never yet attempted to be drawn with accuracy †, is that between species, the occurrence of which in this country at one time or another there is no ground for questioning, and others whose claims to be considered as British have not yet been made substantially good. In distinguishing between these two classes, the author has generally been guided, at least in the case of Birds, by the fact of the existence or not of British-killed specimens in any known collection, or by the comparative recency of the occurrence of any species, and the circumstances under which that occurrence has been announced. Species which are not to be found in any of our Museums, for which no authority is known, or whose claims rest on statements made many years back, at a time when specific differences were but little attended to, he has no hesitation in saying, ought to have a separate place allotted to them as doubtful natives, and not to be mixed up with others which labour under no uncertainty of this nature.
* Several cases might be mentioned of species, which only a few years back had occurred but in a single instance, and which have since been met with more than once.
† This is said with reference only to the Vertebrate Division of the British Fauna. Mr. Stephens has taken great pains to draw the line spoken of in the rase of our native Insects.
Another line which the author has attempted to draw, is that between what may be termed good or genuine species, and such as are probably not distinct from others, or which are involved in some obscurity from the circumstance of their true characters not being well understood. In this latter division he has placed such animals as the Catodon Sibbaldi of Fleming, the Red Lark of Lewin the Lacerta cedura and L. anguiformis of Sheppard, the Comber Wrasse of Pennant, the Lesser Fork-beard of Jago (Raniceps Jago, Flem)., and a vast many others, especially amongst the Fish, all which he would designate as doubtful species; but he has not placed in it animals, such as the Exocostus and Hippocampus which are perfectly good species, as well as undoubtedlv British, but of which the exact species met with in our seas or islands remains to be determined*. These are often cases in which it was not supposed that more than one species existed, at the time of their being enrolled in the British Fauna.
It must now be explained in what way these and other divisions, under which the Animals of this country may be parcelled, are distinguished in the present work. For this purpose recourse has been had to different types, and to two distinct sets of numbers. Firstly, all those well-ascertained, or at least genuine species, which are met with at the present day, or which have undoubtedly occurred at one time or another within the record of history, have one continuous numbering in each Class respectively, and form what may be termed the body of the work*. These are then divided into, firstly, such as are found now existing in a truly wild state; secondly, such as are domesticated, or, when at large, are supposed to have been originally introduced into these Islands; and thirdly, such as were indigenous in former times, but are now extirpated. In the case of the truly wild and now existing species, which of course constitute the great bulk of the Fauna, and which may be subdivided by those who please into Residents, Periodical Visitants, and Stragglers, the names and specific characters are printed in Small Pica; the synonyms and descriptions in Bourgeois. In the case of the domesticated, naturalized, and extirpated species, these types are exchanged for Bourgeois and Minion respectively; the first two are, however, particularly distinguished by having an asterisk (*) prefixed to their names, the last by a dagger (†) in like manner. The second principal division comprises the doubtful natives and doubtful species, which terms are employed in the sense in which they have been already explained. These, although inserted in their proper places in the system, are cut off, as it were, from all those above mentioned, and marked by a distinct numbering enclosed in brackets. The types resorted to are the same as those adopted in the case of the naturalized and extirpated species, but these types are here set a little way in from the margin. By such an arrangement the attention is more readily drawn to these animals which stand in such particular need of further investigation by the naturalist.