254 CLASSIFICATION OP FISHES. 



tion we have been guided entirely by outward structure ; 



since the different modifications of the teeth^ asM. Cuvier 

 himself confesses^ ^' are varied in the most surprising 

 manner ; " so that almost every species differs from its 

 congener^ and proves the utter futihty of attempting 

 to make them the bases of generic characters. Now, 

 as the form of the body and fins partakes also^ in 

 some degree^ of this unusual variation, it may be 

 better to view this division as assuming the rank of a 

 sub-family^ and to consider the above-mentioned groups 

 as genera^ rather than as sub-genera : this will enable 

 us to specify the minor types^ and to designate them, we 

 hope, in a more comprehensible manner than has 

 hitherto been done. 



(223.) The Characincp, or tropical salmon^ appear 

 typically represented by the genus Serrasalmo of Lace- 

 pede. These are a group of large, stout nsh^ whose depth 

 is more than half as much as their length : the snout 

 is blunt : the head small ; the gills very large^ bony^ and 

 naked : the mouth opens obliquely downward : the upper 

 jaw is small ; but the lower one is excessively thick and 

 strongs being armed with sharp triangular cutting teeth 

 double the size of those in the upper jaw : the pectorals 

 are placed very low^ close to the belly ; and the ventrals, 

 which are only half as large, are immediately under 

 the first dorsal fin ; and both these latter are pointed : 

 the anal is long, broad in front, and gradually nar- 

 rowed behind : the scales are small ; and the belly is 

 sharp and dentated like the teeth of a saw : in some_, 

 as in S. nigricans (Spix, pi. SO.), there is a very short 

 procumbent spine, pointing forwards, at the base of 

 the first dorsal ; while, in others, as in S. ferox Nob. 

 (Spix, pi. 28.), these anterior spines point backwards, 

 and three or four of the first dorsal rays are spinous. 

 Those fishes which form the sub-genus Myletes Cuv., 

 have all the above characters, except that the procum- 

 bent spines are wanting, the teeth are blunt, and 

 the upper jaw is strongly angulated. The sub-genus 

 Tetragonopterus of Artecli differs only from the last in 



