ORDERS OF FISHES. 127 



nivoroiis in their habits, and often attained a very large size, 

 and they have been detected in comparatively large num- 

 bers on the same geological horizon both in Europe and 

 North America. In this family the first ray of the pectoral 

 fins forms a formidable defensive weapon ; but the most 

 striking character is found in the greatly - developed and 

 powerful teeth, which may be equal or unequal in size, and 

 are sometimes cylindrical, sometimes compressed and lancet- 

 shaped. 



Sub-order B. Anacanthini. — This sub-order is distin- 

 guished by the fact that the fins are entirely supported by 

 " soft " rays, and never possess " spiny " rays ; whilst the 

 ventral fins are either wanting, or, if present, are placed 

 under the throat, beneath or in advance of the pectorals, 

 and supported by the pectoral arch. The swim -bladder 

 may be wanting, but when present it does not communicate 

 with the oesophagus by a duct. 



The only important families in this sub-order are the 

 Gadidoi (Cod family) and the Pleuronectidce (Flat - fishes). 

 The Gadidce comprise the living Cod, Haddock, Whiting, 

 &c., and appear to date their existence from the Eocene 

 Tertiary. The PleiironedidcB comprise the living Sole, 

 Flounder, Plaice, and the like, in which the body is very 

 much compressed from side to side, and is bordered by long 

 dorsal and anal fins. The bones of the head are twisted in 

 such a manner that both eyes are brought to one side of the 

 body. The fish keeps this side uppermost, and is dark- 

 coloured on this aspect ; whilst the opposite side, on which 

 it rests, is white. The mouth has the two sides unequal, 

 the pectorals are rarely of the same size, the ventrals look 

 like a continuation of the anal fin, and the branchiostegal 

 rays are six in number. The Pleuronectidce are only known 

 by two or three fossils, of which the oldest is the little 

 Rhorribus minimus (fig. 496) of the Eocene deposits of Monte 

 Bolca. 



Sub-order C. Acanthopteri. — This sub-order is char- 

 acterised by the fact that one or more of the first rays in 

 the fins are in the form of true, unjointed, inflexible, 

 " spiny " rays. The exoskeleton consists, as a rule, of 



