OSTARIOPHYSI 595 



Callichthys. There are other sexual differences in many species 

 of Plecostomus, Chaetostomus, and Loricaria, as the presence of 

 dermal tentacles on the snout (see Pig. 359), or of hair-like 

 bristles on various parts of the head and fins in the males, which 

 are usually of larger size. 



About 200 species are known, all from the tropical and sub- 

 tropical parts of Central and South America. The largest species 

 (Chaetostomus gigas) measures 1\ feet ; many are of very small 

 size.^ The genera may be referred to two sub-families : — 



(i.) Akginae. — Body naked ; ribs strong. Arges, Stygogenes, 

 Astroilepus. 



(ii.) LORICARIINAE. — Body cuirassed by bony plates ; ribs very 

 slender. Plecostomus, Liioosarcus, Chaetostormis, Cochliodon, 

 Pterygoplichthys, Rhinelepis, Acanthicus, Otocinclus, Hypopto- 

 poma, Loricaria, Acestra. 



Fig. 360. — Acestra gladius, from the Jurua River, with upper and lower views of 

 head and truiilt. (§ nat. size.) 



The " Prenadillas " of the Andes, Arges and Stygogenes, were 

 believed to live in subterranean waters within the bowels of active 

 volcanoes, and to be ejected with streams of mud and water during 

 eruptions, a story that has been repeated by Humboldt. The 

 fact is that they live in small torrents at great altitudes (up to 

 10,700 feet), and are swept down during periods of disturbance 

 caused by the eruption of the volcano.^ The members of the sub- 

 family Loricariiuae vary much in the shape of the body, which 

 may be short and stout, or more or less slender, the extreme in the 

 latter respect being attained by the species of the genus Acestra. 



^ A monogi'aph of these Fishes, by Mr. C. T. Regan, will shortly appear in the 

 Transactions of the Zoological Society. 



2 Cf. Jloritz Wagner, Abh. Alcad. Milnch. x. 1866, p. 101, and Whymper, Trav. 

 Andes Ecuador, 1892, p. 251. 



