ICHTHYOLOGY. 3 



ciple of classification is that adopted by M. Agassiz, who 

 divides them into Four Classes according to the forma- 

 tion of their Scales, thus — 1. The Placoid, or flat-scaled 

 (from the Greek 7r\.a/cov?, a flat cake) ; 2. the Ganoid, 

 or polished-scaled (from the Greek <y a v6a>, to polish) ; 

 3. the Ctenoid, or tooth- scaled (from the Greek /crew, 

 a comb) ; 4. the Cycloid, or circular-scaled (from the 

 Greek icu/cko?, a circle). To the first, or Placoid class, 

 belong sharks, dog-fish, skates, and other cartilaginous 

 fish, or fish without real bones ; to the second, or Ganoid 

 class, belong the sturgeon, who is also cartilaginous 

 but " armour-plated" with bony plates, and many fish 

 now only known to us in their fossil state. To the 

 third, or Ctenoid class, belong perch, pope or ruff, and 

 pike ; and to the fourth, or Cycloid class, carp, salmon, 

 eels, and most of our edible fresh and salt-water fish. 

 Many valuable characteristics of fish have been ascer- 

 tained from the formations of their Scales, as also from 

 the disposition of the Teeth, which are respectively 

 situate upon the jaws,, palate, tongue, and throat, 

 and severally constructed for prehension, cutting, or 

 crushing, thus indicating the character of food mostly 

 taken by the several species. The age of fish may also 

 be ascertained from their scales when examined under a 

 strong microscope. 



For the purpose of angler-naturalists who do not care 

 to go very deeply into ichthyology it will suffice to divide 

 fish into the two great Orders of Acanthopterygii and 

 Malacopterygii, which (derived from Greek words) re- 

 spectively signify " Spiny or prickly- finned " and " Soft- 

 finned" fish. Of the different fish with which I deal in 

 these " Notes," the perch, the ruff, the bull-head, and the 



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