586 



TELEOSTEI 



Gastromyzon of North Borneo, in which the pectoral and ventral 

 fins are much expanded to form, with the belly, a sucker by 

 which the fish adhere to the stones of mountain torrents, showing 

 a remarkable analogy to Jlxostoma among the Silurids.^ 



Fig. 355. — Gastromyzon borneeiisis, ventral view, natural size. 



Fam. 4. Siluridae. — Mouth non-protractile, bordered by the 

 praemaxillaries and the maxillaries, or by the praemaxillaries 

 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 

 (parieto-occipital) ; symplectic and suboperculuni absent. Pha- 

 ryngeal bones normal, with small teeth. Eibs 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 inter- 

 neural bones. The pterygials or supports of the pectoral rays 

 are large and reduced to two or three.^ Teeth are rarely present 



' On the anatomy of the Cyprinids, of. Sagemehl, Mor]p}iol. Jahrb. xvii. 1891, 

 p. 489. 



^ Cf. Boulenger, " Poissons du Bassin du Congo," p. 238 (1901). 



^ In Exostoma these bones are two in number and so elongate as to resemble the 

 condition characteristic of the Pediculati. 



