6 FISHES OF AUSTRALIA. 



weak, jointed, and often cartilaginous ; these, likewise. 

 being connected by a thin membrane. Spines are present 

 in one or more of the fins of all so-called spiny-rayed 

 fishes, such as the Black Bream, the Tailer or the Mullets ; 

 and even amongst the "soft-finned" fishes certain forms 

 occur, in which single spines are developed on certain of 

 the fins. Familiar instances of the latter are the Cat- 

 fishes, with their large and dangerous spines in the dorsal 

 and pectoral fins. 



The dorsal fin is situated along the middle of the 

 back. In many cases there is only the one this being 

 very short as in the Herrings, long and continuous as 

 in the Parrot- Fishes, or of an intermediate nature while 

 in others, such as certain Perches, Mullets, etc., two are 

 to be found ; excepting in the case of Sharks and Rays, the 

 first being known as the hard or spinous dorsal, and the 

 second, the soft or rayed dorsal. In certain fishes, like 

 the Sergeant Baker, the Salmon-Catfishes and the 

 Trouts, which only possess one main dorsal fin, there is 

 a second and generally very small,* fleshy one on the 

 back, in the region of the tail; this being known as the 

 adipose fin. In fishes of the Mackerel family, and also 

 in some others, there are to be found both spinous and 

 rayed dorsals ; with also, succeeding the latter, a number 

 of tiny fins called finlets. These may really be con- 

 sidered as single detached rays, excessively branched 

 from their insertion on the back, where they are remark- 

 ably thick and fleshy. 



Upon a study of the dorsal fins of fishes, illustrated 

 within even this little work, being made, it will be found 

 that an immense variety in form exists. In the accom- 

 panying illustration, the dorsal fins of a few of our com- 

 mon edible fishes are figured; and, though more widely 

 divergent forms could readily be chosen, they will suffice 

 to show the reader what a great diversity of shape is to 

 be found. 



The dorsals, as well as the other fins, among the 



* In many tropical species of Cat-fishes, the adipose dorsal fin is 

 exceedingly large. 



