126 FISH GALLERY. 



Halosauriformes. 



The Halosauriformes or Heteromi constitute a small suborder 

 of fishes, mostly confined to the deep seas. The pelvic fins, if 

 present, have many fin-rays (about 10) and are set far back 

 (abdominal position) ; the pectoral fins are set high up the sides 

 of the body; the right and left parietal bones meet. The 

 mesocoracoid bone in the shoulder-girdle is reduced or absent ; 

 the post-temporal bone is small and simple. The suborder 

 includes the families Halosauridse, Notacanthidse, Dercetida? 

 (extinct; Cretaceous), and Fierasferidse. 



The Halosauridse and Notacanthidse are long-bodied, deep-sea 

 fishes, with tail tapering to a point and without a separate caudal 

 fin. The body is clothed with cycloid scales, which extend also 

 partly over the head. In the latter family (e. g. Notocanthus, 

 420) the dorsal fin is represented by a series of short, isolated 

 spines ; the anal fin is long, the front part supported by spines, 

 the hinder part by soft rays. In the Halosauridse (e. g. 419) 

 there are no spines ; the dorsal fin has a short base, the anal 

 a long base. 

 Fierasfer. Fierasfer (421) is a strange little fish which lives in the bodies 

 of holothurians, starfishes and bivalve molluscs, particularly 

 the Pearl Oyster. It is not a parasite, so far as our present 

 information goes, but catches its own food from the sea water, 

 and enters and leaves the body of its host repeatedly without 

 apparently causing any inconvenience. Fierasfer is found near 

 the coast in all warm and tropical seas. It has a long tail, 

 with extended dorsal and anal fins reaching to the extremity, 

 which has no separate caudal fin. The anus is far forward, in 

 the throat region ; there are no scales and no pelvic fins. 



Gastrosteiformes (Sticklebacks and Sea-horses). 



The suborder Gastrosteiformes or Catosteomi includes curious 

 fishes, the affinities of which have been the object of much dis- 

 cussion. The least aberrant forms are the Sticklebacks, with 



