142 LOWER VERTEBRATES. 



When the month is closed, these large teeth remain outside. The other species have 

 smaller teeth. All of them inhabit considerable depths, and are provided with luminous 

 spots of the complex stomiatoid type. Some of them are silvery, others black in 

 color, the latter probably inhabiting the greater depths. Chauliodus sloani seems to 

 be comparatively common in the mid-Atlantic. It has been longer known than any 



other species which inhabits 

 waters so deep. 



The Halosaueid^ are elon- 

 gate fishes, bearing a super- 

 ficial resemblance to the Ma- 

 cruiidse :md other Anacanthine 

 forms, Mhich, in structure, are 

 very different. There are no 

 barbels; the head and body 

 Fig. 91.— Chauliodus sloani. are seal}'. The maxillaries 



form the border of the upper 

 jaw ; the teeth of the mouth are all small. There is no adipose fin ; the dorsal 

 fin is short and small, and the anal fin is ^ery long. The tail is long and tapers 

 to a point, there being no separate caudal fin. The species are black in color, and are 

 provided with phosphorescent spots. Five species are known. They are apparently 

 abundant in the depths of the Atlantic, and one of them {Halosaiirus macrochir), has 

 been several times taken at great depths off our coast. They reach a length of about 

 two feet. The extinct family of Hoplopleueid^, found in cretaceous and tertiary 

 rocks, is placed near the Halosaurida; by Dr. Gilnther. In this group, the body 

 is armed "with four series of subtriangular scutes, besides intermediate scale-like 

 smaller ones." 



The Paktodontid^e comprises but a single known species {Pantodon buchhohi), a 

 small, fresh-water fish from the west coast of Africa. It is said to resemble a Cyprinodont, 

 but with the sides of the head osseous, and the subopercle and interopercle obsolete. 

 The NoTOPTEEiD^ are fresb-water fishes of the East Indies and western Africa. 

 They have the body elongate, ending in a long and tapering tail. The belly has a 

 double serrature and some of the bones of the head are also serrate. There is no adipose 

 fin. The dorsal fin is very small or wanting, and the anal, as in the Halosauridfe, is 

 very long. The subopercle is wanting. The teeth are small. The air bladder is 

 highly complex in structure, being " divided into several compartments, and termina- 

 ting in two horns anteriorly and posteriorly, the anterior horns being in direct connec- 

 tion with the auditory organ." 



The OsTEOGLOSSiD^ are large, pike-like fishes of the rivers of the tropics. The 

 head is naked and its skin is ossified so that it is almost entirely covered by bone, 

 somewhat as in the genus Amia. The scales on the body are very hard and bony, 

 composed of pieces like mosaic. The mouth is large, but the teeth are small. The 

 dorsal and anal are long, and placed far back, near the small caudal. The air-bladder 

 is sometimes cellular. One genus (Osteoglossum) has two barbels on the lower jaw, 

 and the edge of the abdomen is trenchant. The others have the abdomen rounded and 

 the mouth without barbels. Six species of these remarkable fishes are known. 

 Arapaima gigas inhabits the rivers of Brazil and Guiana, where it is said to reach a 

 length of fifteen feet and a weight of four hundred pounds. It is the largest strictly 

 fresh-water fish known, and in Brazil it has considerable economical importance as a 



