THE CHIMERAS. ORDER GANOIDEI. 39 



Plagiostomi, as already stated, in the arrangement by which the 

 water passes away from the branchiae ; the branchite themselves 

 have the same structure as those of the Sharks, but the five pass- 

 ages which convey the water from the branchial chambers 

 unite so as to form a common external orifice, which is covered 

 by a sort of rudimentary operculum. Thus these curious Fishes 

 evidently form a transition towards those which are constructed 

 on the ordinary type, in which the gills are free and covered by 

 a movable operculum. The vertebral column in these Fishes is 

 represented by a chorda dorsalis ; the upper jaw is wanting, and 

 the superior teeth, of which there are four, are supported upon 

 the front of the cartilaginous skull ; the lower jaw has only two 

 teeth. They are oviparous, and lay large, flattened eggs, en- 

 closed, like those of the oviparous Sharks and Rays, in a strong 

 horny case. 



591. The best known species is the Northern Chimcera, an 

 inhabitant of the seas of high northern latitudes, which occurs, 

 however, occasionally upon our shores. It is a Fish of a most 

 extraordinary aspect, of a silvery colour, spotted with brown, 

 with an obtusely conical snout, and a very long tapering tail. It 

 usually measures three or four feet in length, and feeds princi- 

 pally upon small fishes, usually following the shoals of Herrings 

 in their migrations ; from which circumstance it has received the 

 name of the King of the Herrings. It also feeds on Crustacea 

 and other small marine animals. Another species is found in 

 the southern seas, which is rendered remarkable by a singular 

 cartilaginous process at the extremity of the snout, bearing some 

 resemblance to a hoe. 



ORDER II. GANOIDEI. 



592. The order of Ganoid Fishes includes some remarkable 

 living forms, which appear to constitute an intermediate group 

 between the Cartilaginous Fishes just described and the Osseous 

 or typical Fishes. The number of these Fishes now in existence 

 is small, but in early periods of the geological history of our 



