586 TELEOSTEI CHAP. 
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 Hxostoma among the Silurids.’ 
Fic. 355.—Gastromyzon borneensis, 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 subopereulum absent. Pha- 
ryngeal 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 
pais 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, cf. Sagemehl, Morphol. Jahrb. xvii. 1891, 
p. 489. 
* Cf. Boulenger, ‘‘ Poissons du Bassin du Congo,” p. 238 (1901). 
3 In Exostoma these bones are two in number and so elongate as to resemble the 
condition characteristic of the Pediculati. 
