254 CLASSIFICATION OF 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 futility 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. 



(228.) The CharacirwBj or tropical salmon, appear 

 typically represented by the genus Serrasalmo of Lace- 

 pede. These are a group of large, stout fish, 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 

 strong, 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 Artedi differs only from the last in 



