CAT-FISHES. 575 



{very rarely in front of) the dorsal. The gill-membranes are 

 confluent with the skin of the isthmus, the gill-opening heing 

 reduced to a short slit. Pectorals and ventrals horizontal. 

 Vent hefore, or not much behind, the middle of the length of the 

 lody. 



a. Hypostomatina. 



Stygogenes. — Adipose fin short ; dorsal and anal short ; 

 the outer fin-rays somewhat thickened and rough ; palate tooth- 

 less ; cleft of the mouth of moderate width, with a maxillary 

 barbel on each side ; a short broad flap on each side between 

 the nostrils, which are close together. Lower lip very broad, 

 pendent. Eyes small, covered with transparent skin. Head 

 covered with soft skin. Ventrals six-rayed. 



These small Siluroids, wMch are called " Prenadillas " by 

 the natives, together with the allied Arges, Brontes, and Astro- 

 jolebus, have received some notoriety through Humboldt's 

 accounts, who adopted the popular belief that they live in 

 subterranean waters within the bowels of the active volcanoes 

 of the Andes, and are ejected with streams of mud and 

 water during eruptions. Humboldt himself considers it very 

 singular that they are not cooked and destroyed whilst they 

 are vomited forth from craters or other openings. The ex- 

 planation of their appearance during volcanic eruptions is, 

 that they abound in the numerous lakes and torrents of 

 the Andes, that they are killed by the sulphuretted gases 

 escaping during an eruption, and swept down by the torrents 

 of water issuing from the volcano. 



Callichthys. — Adipose .fin short, supported anteriorly by 

 a short movable spine ; dorsal with a feeble spine and seven or 

 eight rays ; anal short. Teeth minute or entirely absent ; cleft 

 of the mouth rather narrow, with a pair of maxillary barbels on 

 each side, which are united at the base. Eyes small. Head 

 covered with osseous plates ; body wholly protected by two 

 series of large imbricate shields on each side. Ventrals six-rayed. 



