2882 THE BONY FISHES AND GANOIDS 



stone Pennine chain in the north, and the Red Sandstone districts of the central 

 counties, and likewise in the chalk streams of the south. In the latter area grayling oc- 

 casionally run to nearly four pounds in weight, but in Northern Scandinavia they may 

 reach one pound more. In Switzerland they are found in Lake Constance and other 

 large pieces of water. An elegantly-shaped fish, the grayling varies considerably in 

 color according to the season of the year, the back being generally greenish brown, 

 passing into gray 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-gray 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 some- 

 times also the latter, being ornamented with longitudinal dark bands or rows of 

 spots. A second species, with smaller scales, inhabit the mountain streams of Dal- 

 matia, but the other two are North American. 



A remarkable fish from the fresh waters of the United States known 

 as Percopsis guttata, which has the general characteristics of a salmon- 

 oid but the mouth and scales of a perch-like type, is regarded as representing a 

 family (Percop sides'} by itself, nearly allied to the salmon tribe. 



THE BONY PIKE AND ITS KINDRED SUBORDER ^Etheospondyli 



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

 edly lower type of organization than those described above; and, although the stur- 

 geons 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 

 pike of the fresh waters of North America constitute a family (Lcpidosteidtz) which 

 forms the sole existing representative of a distinct suborder. While agreeing with 

 the preceding suborders in the divisional characteristics mentioned on p. 2702, 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 dis- 

 tinctly overlapping. In the living representatives 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 inter- 

 lacing 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 ossi- 



