490 



PISCES SUB-CLASS III.TELEOSTOML 



hedgehog ; therefore they are frequently called sea-hedgehogs. However, it 



is probable that the spines 

 are a protection not only 

 when the fish is on the sur- 

 face and able to take in air, 

 but also when it is under 

 water." The third sub-family 

 of the Diodontidce includes 

 only the two species of sun- 

 fish, Orthagoriscus, specimens 

 of which at times grow to as 

 much as seven feet in length. 

 Having the body excessively 

 compressed and deep, with a 

 very tall dorsal and anal fin 

 placed one above the other 

 at the hinder end, the sun- 

 fishes are especially charac- 

 terised by the short, deep, 

 and truncated tail, of which 



fig. 21. COMMON SUN-FISH. the fin is confluent above with 



the base of the dorsal, and 



below with that of the anal. There is no dilatable sac beneath the skin, 

 which may be either rough or smoothly tesselated ; and externally the 

 pelvic fins and internally the air-bladder are absent. Sun-fish are pelagic 

 forms, generally swimming in a vertical position near the surface of the 

 water. Both kinds seem to feed chiefly on shell-fish. 



SUB-ORDER IV. AXACANTHINI. 



The members of this comparatively small, although highly important 

 sub-order are distinguished from the Acanthopterygii by the pelvic and 

 median fins being, as a general rule, devoid of spines and composed of soft 

 jointed rays. When present at all, the pelvic fins are invariably either thor- 

 acic or jugular in position ; and in those forms furnished with an air bladder, 

 this has no communication with the oesophagus. 



The first four families of the sub-order form a section known as the Ga- 

 doidei, and are characterised by the normal and symmetrical form of the head 

 and body. The family of the Lycodidce includes several 

 Family genera of blenny-like fish characterised by the union of all 

 Lycodidce. the median fins, and by the pelvics, when present, being 

 small, jugular, and articulated to the pectoral arch. Most of 

 these fishes are inhabitants of the seas in the neighbourhood of the two poles. 

 Passing by the family with the bare mention that Lycodes and Gymnelis are 

 two of the best-known genera, we turn to the much more important cod 

 family. In these the caudal fin is generally distinct from the others, but 

 when it is united therewith, the first dorsal is divided, so 

 Family Gadidce. that three dorsals are produced. Generally the pelvic fins 

 which are jugular are well developed, but in those in- 

 stances where they are filamentary, the first dorsal is double. There may 

 be either a single or a double anal. As regards their internal anatomy, it 

 will suffice to say that the cods generally have an air-bladder ; while as their 



