CLASS FOURTH. 

 FISHES. 



Vertebrated animals with cold red blood, and respire by means of gills 

 or brauehiae, and progressing in water by means of fins. 



For an account of the physiology and general characters of fishes, see vol. 

 iii. p. 440, 487, 527, &c. 



There have been many attempts at tlie classification of fishes, both by arti- 

 ficial systems and also from natural arrangements, but that of Cuvier seems 

 the best which has yet been adopted. It is that system which we have given 

 in the following outline. 



Cuvier divides all fishes into two sub-classes, namely : — 



SUB-CLASS I.— CARTILAGINOUS FISHES. 



It consists of three orders : 

 Order I. CycLosTOMi.— II. SELAcaii.— And, III. Sturiones. 

 SUB-CLASS II.— OSSEOUS FISHES. 



It consists of six orders : — 



IV. Pl.ECTOGNATHI.— V. LOPHOBRANCHII. — VI. MaLACOPTERYCII ABDO. 

 Ill IN ALES.— VII. MALACOPTERYCII SUBRACHIATI.— VIII. MaLACOPTERVGIB 

 APoDES. — IX. ACANTHOPTERVGII. 



SUB-CLASS I. — CARTILAGINOUS FISHES, 



ORDER I.— CYCLOSTOMI. 



Jaws fixed in an immoveable ring; brauchi;c adhering, with numerous 

 openings. 



This Older consists of three genera ; namely, 1. Petromyzon ; 2. Ammoce- 

 tes ; and 3. Gastrobranchus ; of which we have figured, 



Petroimizon Jluviatiiis.— The Lesser Lamprey. Plate liii. fig. 1. De- 

 scribed, vol. iii. p. 510. 



GastrobrwicJius ccECUS.— The Glutinous Hag. Plate liii. fig. 2. Body sil- 

 very iridescent-white, with reddish reflections towards the head and tail ; 

 furnished with a double row of lateral pores. Six inches long. Inhabits the 

 European seas. 



ORDER II.— SELACHII. 



liram hi.'e toothed, the openings numerous, without lids or membranes ; 

 palaline aud postinandulary bones provided with teeth, instead of jaws. 



