112 FISH GALLERY. 



eastern Europe ; it is not found in Britain. The Stone Loach 

 occurs in Britain and on the continent, except Scandinavia ; it 

 frequents fast-running streams with stony bottom. 



"at-fislies. The family of the Siluridae or Cat-fishes is a large one widely 



spread over the fresh-waters of the temperate and tropical regions ; 



Wall- a f ew f th e Cat-fishes are found in the sea (e. g. Arius (376), 



and 10. Galeichthys (377) and Plotosus), but they keep near the coast. 

 They are all bottom-feeders, of carnivorous tendencies. The body 

 has no scales, but in many genera it is armoured with bony scutes, 

 more or less sculptured. A strong bony spine is frequently 

 present in front of the dorsal and pectoral fins, and large bony 

 plates occur in the skin at their bases. The spines are sometimes 

 barbed or serrated, and constitute formidable weapons. They are 

 not strictly comparable with the spines of Acanthoptergian fishes, 

 such as the Perch (507, Wall-case 12) and Bass (511, Wall- 

 case 13), since they are formed by the fusion of the pieces of a 

 jointed fin-ray, the fusion taking place during the growth of the 

 fish. One to four pairs of barbels usually occur around the 

 mouth ; an adipose fin is frequently present. 



The division of the family into subfamilies and genera is based 

 upon the extent of the dorsal fin, the presence or absence of an 

 adipose fin, and the fusion of the lower parts of the gill -covers 

 with the " isthmus " under the throat, or their freedom from it. 

 In Clarias (359) and Copidoglanis (361), for instance, the dorsal 

 and anal fins are long-based and extend to the tail-fin, whereas in 

 the other forms shown the dorsal fin is short-based. The anal 

 fin is long-based in Silurus (364), Wallago (367), Silondia 

 (368), but not in Amiurus (373), Rita (371), &c. An 

 adipose fin is present in the last two, and in Doras (379), 

 Synodontis (381), &c, but is wanting in Silurus (364), Silondia 

 (368), &c. In the Electric Cat-fish, Malopterurus , 386, an 

 adipose fin is present, whereas the anterior dorsal fin supported 

 by fin-rays is wanting. 



Some Siluroids are provided with an accessory breathing organ. 

 Clarias (359, and fig. 55) and Heterobranchus have a dendritic 

 organ situated above the gills which enables the fish to live out of 

 water for some time. In the dry season these fishes live in burrows 

 in the mud and crawl out at nights in search of food. In Sac- 



