276 SILTJK1D2E. 



SILURID^. 



Mouth non-protractile, bordered by the praemaxillaries and the maxillaries, or by 

 the prsemaxillaries only, the maxillaries being often rudimentary and supporting the 

 base of a barbel; jaws usually toothed. Parietal bones usually confluent with the 

 supraoccipital, forming a single large plate ; symplectic and suboperculum absent. 

 Pharyngeal bones normal, with small teeth. Ribs attached to the lower surface 

 of long parapophyses ; epipleurals absent. Pectoral fins inserted very low down, 

 folding like the ventrals, often armed, like the dorsal, with a strong bony spine. 

 Body naked or with bony plates. An adipose dorsal fin often present. One to four 

 pairs of barbels. 



The skull and the opercular apparatus show a reduction in the number of elements 

 as compared with the Characinids and Cyprinids, such as the absence of the 

 metapterygoid, the often rudimentary rod-like condition of the palatine, and the 

 fusion of the parietals with the supraoccipital. The scapular arch is solidly united to 

 the skull and is often very massive, and the occiput may be connected with the base of 

 the dorsal fin by a buckler formed by the expansion of the first and second interneural 

 bones. The pterygoids or supports of the pectoral rays are large and reduced to two 

 or three. The branchiostegal rays vary from 4 to 17. Some of the anterior vertebra? 

 may be solidly fused together and also with the occipito-nuchal buckler ; the complex 

 which follows the first vertebra, w 7 hich is more or less rudimentary, if distinct, 

 represents the fusion of the second, third, and fourth vertebrae ; the first, strongly 

 developed, transverse process represents that of the fourth vertebra. The air-bladder 

 is usually large and trilocular, but additional septa may greatly complicate its 

 structure * ; it may be more or less reduced and entirely or partially enclosed in a 

 bilateral bony capsule formed by the transverse processes of the vertebrae. The 

 intestinal tract may be simple and short, or extremely long and convoluted ; as in the 

 Cyprinids, pyloric appendages are absent. 



Cat-Fishes, as Silurids are usually called, are a large family embracing some 

 one thousand species, spread over the freshwaters of all parts of the world, but mostly 

 from between the tropics. Only a few are marine. 



Nearly two hundred species, referred to thirty-seven genera, are known from Africa. 

 Fifteen genera are represented in the Nile system and may be grouped under five 

 subfamilies, as shown in the following synopsis. 



* Of. Bridge & Haddon, Phil. Trans. E. Soc. elmiv. 1893, p. 65. 



