It may be added that in computing the fin-ray formula, which is similar to that adopted by MM. Cuvier and Valenciennes, all the rays are included which it was possible to distinguish, on the ground that if the short rays be omitted, which often pass insensibly into the longer ones, it were difficult to know where to begin the reckoning. The mention of this circumstance will serve to explain why the number of fin-rays as stated in this work will be often found to exceed the number given by former authors, who appear in general to have made their computation without . much attempt at accuracy. The above remark, however, does not apply to the caudal fin, in which, generally, though not always, there is a tolerably well marked line of separation between what may be termed the principal rays, and the accessory or shorter ones. In many instances, in which this distinction is evident, these two kinds of rays are reckoned separately.

Appended to the description of each species, are a few general remarks illustrative of its habits; more especially those connected with locality, food, and propagation. It was thought that these would render the work more generally useful. Many of them are the result of the author's own observation, though some are confessedly obtained from other sources.

On the subject of Classification, it must be remarked that the system of no one individual author has been rigidly adhered to. Regard has been paid to what has been written on this subject by the most recent writers in each department, and all the larger groups, as well as, in most instances, their mode of collocation, have been derived from such sources. The arrangement of the Mammalia has been drawn up from a combined view of the system of Cuvier, and the systems of Gray * and MacLeay †. That of the Birds from a similar view of the system of Vigors ‡, and the modifications of that system as adopted by Swainson and Selby; assistance has been also gained, in regard to the situation of a few genera, from the system of Lesson *. The arrangement of the Reptiles and Amphibious Animals is for the most part in accordance with that in the "Regne Animal" of Cuvier. The author has, however, followed Latreille and many modern naturalists in considering these groups as two distinct classes. The arrangement of the Fish is likewise similar to that in the second edition of the "Regne Animal," excepting a slight alteration in the value of the larger groups, adopted from the Prince of Musig-nano†. In no case must it be imagined that the order of affinities is exactly the same as the order of arrangement given, since, if it be true that all natural groups be circular, an opinion now generally prevalent, and one in which the author is strongly disposed to join, it is clearly impossible to preserve such a coincidence under circumstances which necessarily entail the appearance of a linear series.

* Ann. of Phil. vol. xxvi. p. 337. † Linn. Trans, vol. xvi. p. 1, etc.

‡ Linn. Trans, vol. xiv. p. 395. See also some Articles by the same author in the first and second volumes of the " Zoological Journal".

The author has also exercised his own judgment in the adoption of certain genera and sub-genera. With respect to these last, having expressed his views elsewhere ‡, it is unnecessary to repeat them in this place. He may simply state that he has endeavoured to acknowledge, and to act up to, the principle which he has there advocated; although, from the ignorance in which we are upon the subject of the real value of many groups, it cannot be doubted that numerous instances occur, in which he has failed making a correct application of it. Being aware of the dislike which many of our own naturalists have to the adoption of sub-genera, he begs to state that they are inserted in such a manner, that any one who chooses may place them upon the same footing with the genera, or, if he be not a friend to the subdivision of the old-established groups, take no notice of them at all.

* Traitt of Ornithologie; ou Tableau methodique des Ordres, Sous-ordres, Families, Tribus, Genres, Sous-genres et Races d'Oiseaux. Par. 1831. 8vo.

† Saggio dl una Distribuzione metodica degli Animali Vertebrati. Rom. 1831. 8vo. The alteration above alluded to has been adopted by the author since the publication of his "Systematic Catalogue".

‡ Loud. Mag. of Nat. Hist. vol. vi. p. 385. and vol. vn. p. 97.

Instead of prefixing the generic characters to the several genera respectively as they occur in order, they are presented in a synoptic form at the head of each of the Classes, by which means a better view is obtained of the relative collocation and affinities of the larger groups. Moreover, the same kind of arrangement with respect to types prevails here, as that which occurs in the other part of the work. The characters of all those genera and sub-genera which contain truly wild, as well as genuine and now existing species, are printed in Small Pica and Bourgeois respectively, the names of the genera standing in LARGE CAPITALS, those of the sub-genera in small capitals. In the case of the domesticated, naturalized, and extirpated animals, these types are exchanged respectively, as before, for Bourgeois and Minion; the first two, being, also in like manner, particularly distinguished by an asterisk, the last by a dagger. The same types are employed for the characters of those genera and sub-genera which contain only doubtful natives or doubtful species, but these may be readily distinguished from the last by the circumstance of the names standing in ITALIC Capitals, which are large or small, as in the former instances, according as the group in question is either a genus or sub-genus. Moreover, in this division, the genera have a distinct numbering enclosed in brackets: the sub-genera no numbering at all. It may be further observed, that the characters of the orders and families are printed in Pica, and that 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.