138 HYPOSTOMA. 



divisions have been made in the genus; the first 

 with the body thick and short, and the head dis- 

 proportionally large ; — where the angles of the 

 plates become less developed, and the head becomes 

 depressed ; — and the last, where the inter-operculum 

 is very moveable and is furnished with tufts (as in 

 Acanthicus) of rigid spines which can be displayed 

 at will; when at rest, they are concealed in a 

 furrow or hollow. Of these we have now examples 

 of two, the first and the last. In their outward 

 structure we have a prevalence of the spination and 

 rough armature which seems so remarkably deve- 

 loped in this tribe of fishes, and in them we also see 

 the first trace of the double dorsal fin, analogous to 

 the adipose among the Salmonidae, but differing in 

 the spinous defence which is placed anterior to the 

 membrane. In the habits of Hypostoma^ as in- 

 timated by D'Orbigny, we have a confirmation in 

 many parts in the short notes with which we have 

 been favoured by our own traveller, and which 

 will be stated in the descriptions of the fishes to 

 which they refer. " These fishes (Hypostoma) are 

 always found in the places where the current is 

 most rapid; they conceal themselves in numbers 

 under stones and in the clefts of rocks, and attach 

 themselves there by the suction of their lips, or 

 they fasten themselves on by the hooks of their 

 opercular spines so strongly that it is easier to break 

 them than to tear them off; when touched, they 

 erect their spines to defend themselves. They swim 

 with rapidity, and often with the back undermost, 



