DOKSAL FINS. 25 



with the common skin of the body, that their rays are 

 completely hid^ except in such few as are provided with 

 an anterior spine, which, being obviously employed as 

 an offensive weapon, is consequently naked_, and par- 

 tially unattached to the other rays. The fins of the 

 PleuronectidcB, or flat fish, are nearly as thick as those 

 of the cods ; but the rays, being spinous, are more 

 naked at their extremities. Those lovely fish, the 

 chastodons. have their dorsal fins remarkably thick, and 

 so covered with compact scales, nearly to their margins, 

 that their motion would seem to be very limited. 

 The great majority of thick-finned fishes are found in 

 the soft-rayed order (Malacopteryges), while those of 

 an opposite nature are almost confined to the typical 

 osseous division, or the Acanthopteryges. The dorsal 

 fins of the great tribe of perches, together with those 

 of the Spari, Labri, TriglidcB, Gymnetes, &c., are 

 thin ; that is to say, the rays, whether slender or strong, 

 are not in any way covered by the common skin of the 

 body, but are bare almost to their base, and united by 

 a thin membrane, sometimes, indeed, beautifully coloured 

 and opaque;, as in Serranus, Perca, Labrus, &c., but 

 generally sub-transparent, and almost colourless, as in 

 the whole of the Sparidm, Scomberidce, Zeidce, &c. 



(29.) The number of the dorsal fins is variable ; 

 for although they are all placed upon the same line, 

 which is invariably the ridge or summit of the back, 

 they are yet separated, more or less, into divisions; and 

 these, when perfectly detached one from the other, are 

 viewed in the light of separate fins, although, strictly 

 speaking, they should simply be considered as so many 

 divisions of a single one. Where the intervals are marked 

 by a secession of a connecting membrane between the 

 rays, there is no difficulty in determining whether, ac- 

 cording to the common mode of reckoning, a fish has 

 two or three dorsal fins : but it frequently happens, 

 even in the same genus, that in one species the mem- 

 brane of the last ray of the first dorsal terminates or 

 adheres to the back j while, perhaps, in the very next it 



