506 GANOIDS. 



Sandstone districts of the central counties, and likewise in the chalk streams of the 



south. In the latter area grayling occasionally run to nearly 4 lbs. in weight, 



but in Northern Scandinavia they may reach 1 lb. more. In Switzerland they are 



found in Lake Constance and other large pieces of water. An elegantly-shaped 



fish, the grayling varies considerably in colour according to the season of the year, 



the back being generally greenish brown, passing into grey on the sides, while the 



under-parts are silvery. The sides of the head are yellow, with black spots, which 



also occur on the fore-part of the body ; and brownish grey longitudinal stripes 



run in the direction of the rows of scales. The pelvic and anal fins are violet, 



frequently marked with brown crossbars ; the pectorals are yellow, turning to red 



in the breeding-season ; while the black -bordered dorsal and caudal are generally 



red, although sometimes blue; the former, and sometimes also the latter, being 



ornamented with longitudinal dark bands or rows of spots. A second species, 



with smaller scales, inhabit the mountain streams of Dalmatia, but the other two 



are North American. 



A remarkable fish from the fresh waters of the United States 

 Percopsis. 



known as Percopsis guttata, which has the general characters of a 



salmonoid but the mouth and scales of a perch-like type, is regarded as represent- 

 ing a family {Percopsidoi) by itself, nearly allied to the salmon tribe. 



The Bony Pike and its Kindred, — Suborder ^theospondyli. 



The remaining groups of the Teleostomous fishes exhibit a more or less decidedly 

 lower type of organisation than those described above ; and, although the sturgeons 

 are still well represented, these groups as a whole are evidently waning ones 

 at the present day, having only very few living forms, whereas in past epochs 

 some of them formed the dominant types in the fish-fauna of the world. The bony- 

 pikes of the fresh waters of North America constitute a family {Lcpidosteidai) 

 which forms the sole existing representative of a distinct suborder. While 

 agreeing with the preceding suborders in the divisional characters mentioned 

 on p. 334, the members of this group and the next exhibit much more 

 marked differences from all the foregoing groups than do the latter from one 

 another. With the exception of the extinct spear - beaks, the tail is of the 

 abbreviated heterocercal type ; that is to say, that while its fin is more or less nearly 

 symmetrical, the vertebral column, which retains its primitive tapering extremity, 

 runs in the upper half. The scales are ganoid, and very frequently quadrangular, 

 although they may be rounded and distinctly overlapping. In the living represen- 

 tatives of both suborders the air-bladder is connected with the oesophagus by a 

 duct, in the same manner as in the tube-bladdered fishes ; but the optic nerves 

 simply cross one another, without any interlacing of their fibres, and there is 

 a spiral valve to the intestine. Whereas, with the exception of one extinct 

 group of herrings, the whole of the suborders of bony fishes hitherto noticed are 

 unknown previous to the Cretaceous epoch, members of the two groups to 

 be now considered were abundant in the antecedent Jurassic period. The 

 group including the bony-pike may be distinguished from the next by the full 

 ossification of the internal skeleton ; the scales being always of the typical 



