SILURID^. DIVISIONS OF THE FAMILY. 331 



by the situation of the mouth, which is always placed 

 beneath. The sub-family of PimelodincB next succeeds : 



this is a much more numerous division than the last, from 

 which, although the body is sometimes partially mailed, 

 it may be further distinguished by the mouth being ter- 

 minal, or but seldom placed beneath the snout. It like- 

 wise comprises all those silures whose belly, as in the 

 generality of fishes, is of equal length with the tail, 

 so that the vent is nearly central between the pectoral 

 and the caudal fins : this structure carries with it, 

 almost universally, a peculiarity in the proportionate 

 length of the anal fin, which is never very long, as in the 

 succeeding division ; nor are the number of dorsal fins 

 ever less than two, the hinder of which is always adipose. 

 The third sub- family includes the true Silurince, or 

 anguilliform cat-fish, well represented by the genus 

 Plotosus Bl. (fig. 79«)' They are immediately known 



from the Pimelodi, with which they have hitherto been 

 confounded, by the excessive length of their tail, which is 

 always more than two, and often four, times the length 

 of the abdomen : this structure produces a correspond- 

 ing modification of the ventral fin, which is always 

 exceedingly long and low, so as in nearly all cases to ex- 

 ceed one half the length of the entire fish. Like the 

 Loricarince, we find that the two typical genera of the 

 Silurince are distinguished by the presence or absence of 

 a small adipose fin ; although, in all other respects, their 



