86 MANUAL OF NATURAL HISTORY. 



skeleton/' are employed in the sense in which they 

 are used by Owen, the former meaning the vertebral 

 centre, with the attached bones ; and the latter im- 

 plying the external, or what is often called the tegu- 

 mentary covering of the body. 



V. CLASS.— FISHES (Pisces). 



Live habitually in water ; cold-blooded ; respira- 

 tion aquatic ; skeleton bony or cartilaginous ; body 

 generally covered with scales ; heart bilocular ; no 

 organ of prehension except mouth ; flexure of spine 

 principally lateral ; reproduction oviparous.* 



I. OKDER — Wide-mouthed Fishes (Plagiostomi). 



Endo-skeleton cartilaginous, or partially ossified ; 

 exo-skeleton placoid ; gills with 5 or more gill aper- 

 tures ; no swimming-bladder. 



I. SUB-ORDER.— Rkys (Raiin^). 



Body horizontally flattened, and more or less dis- 



cous ; dorsal fins mostly on tail ; a peculiar (naso- 



pectoral) cartilage, arising from nasal part of skull, 



extends towards or meets anterior part of crest of 



pectoral fin ; branchial openings inferior. 



1. Family. — Horned-Rays (Cephalopteridse). Muzzle 



with two horn-like processes ; mouth before 



or beneath, very broad ; teeth very small, in 



some wanting in upper jaw ; tail as long, or 



longer than body, with a back-fin, and a spine. 



With many exceptions, such as the 'Viviparous Blenny ' (Zoarces 

 viviparus) of our own shores. 



