504 PISCES SUB-CLASS IILTELEOSTOMI. 



and standing up in such a conspicuous manner as to give rise to the name of 

 '* feather-back.'' A better character is, however, to be found in the backward 

 continuation of the anal fin to form a fringe surrounding the tail. There are 

 many other structural peculiarities in these fresh-water fishes, but it will 

 suffice to mention that the air-bladder is divided into a number of compart- 

 ments, and furnished at each end with a pair of prolongations, so that it pre- 

 sents some resemblance to a shark's egg in form. More important, on account 

 of their peculiar geographical distribution, are the small 

 Family fresh-water fishes from the Southern Hemisphere, forming 



Galaxiidce. the genus Galaxias, and typifying a family by themselves. 

 They have the base of the skull single, the pterotic bones 

 solid, and the tail forked or rounded, while there are neither scales, barbels, 

 or a fatty fin, the dorsal being situated directly over the anal fin. The eggs 

 of the female are discharged into the cavity of the abdomen, as in the last 

 family, from which these fishes differ by the simple structure of the air- 

 bladder. The typical Galaxias has long been known from the extremity of 

 South America, Australia, and New Zealand (where, from their spotted 

 coloration, they were formerly known as trout), but it is only recently that 

 a species has been recorded from the Cape. The New Zealand Neochanna 

 of which the known specimens have been found buried in mud far away from 

 water differs by the lack of the pelvic fins. 



This family is noteworthy on account of its containing the largest fresh- 

 water bony fish, the huge Arapaima gigds of the Guianas and Brazil, which 

 attains a length of fully fifteen feet, and a weight of four 

 Family hundred pounds. As a family, the arapaimas are distin- 

 Osteoglossidce. guished from the Galaxiidce, by generally possessing three, 

 instead of two, upper pharyngeal bones. The body of these 

 fishes is invested with unusually large scales, marked with a kind of mosaic- 

 like sculpture, but the head is devoid of scales, and protected by large rough- 

 ened, ossified plates. Wide 

 openings of the mucus canal 

 constitute the lateral line, and 

 the long dorsal fin is placed 

 immediately over the anal 

 to which it is almost similar 

 very far back on the body. 

 Fig. 29. ARAPAIMA. Indeed, so far back are these 



fins, that they sometimes co- 

 alesce with the caudal. The openings of the gills are wide, and both the 

 premaxillse and maxillae enter into the formation of the margin of the upper 

 jaw ; but there are no false gills. Whereas some forms have the air-bladder 

 simple, in others it is composed of cells. Allusion having been already made 

 to Arapaima, we pass on to the typical Osteoylossum, of which there is one 

 species from South America, and a second from Borneo and Sumatra, while 

 the other two are inhabitants of Australia. A pair of barbels to the lower 

 jaw, and the obliquity of the cleft of the mouth, are sufficient to distinguish 

 these large fishes from Arapaima. The flesh is of excellent quality. The 

 last genus, Heterotis, is African, and differs from the other two in having 

 only two upper pharyngeal bones thereby resembling the Galaxiidce and 

 its air-bladder is cellular. The one species is common to the Nile and the 

 rivers of West Africa. 



A fresh-water fish from North America known as the moon-eye (Hyvdon 



