438 PHYSOSTOMI. 



Order III— PHYSOSTOMI, Muller. 



All the fin rays articulated, with the exception of the first in the dorsal and pectoral, which are 

 frequently more or less ossified. Ventral fins, when present, abdominal and spineless. Air-vessel, if 

 existing, having a pneumatic duct (except in the family Scomhresocidri;}. 



SYNOPSIS OP FAMILIES AMONGST THE PHYSOSTOMI. 



1. Sihiriclm. Sub-opercle absent. Margin of upper jaw formed by tbo premaxillaries. Skin scaluless 

 and smooth, or covered with osseous plates or scattered tubercles. Adipose dorsal usually present. 



2. Scopelidee. Pseudobrancbias well developed. Margin of upper jaw formed by premaxillaries. 

 Opercular pieces sometimes incomplete. No barbels. Gill-openings very wide. Scales present or absent. 

 Adipose dorsal present. 



3. Scomhresodda. PseudobrancbiiB glandular. ]\Iargin of upper jaw formed by premaxillaries and 

 maxillaries. Lower pharyngeals united. No adipose dorsal. Scales present. Air-vessel, when present, 

 destitute of pneumatic duct. 



4. Ci/iynnodordidce. Pseudobranchia) absent. Margin of upper jaw formed by premaxillaries. Barbels 

 absent. Teeth in both jaws, in superior and inferior pharyngeals. One spineless dorsal in posterior half of 

 body. Air-vessel simple. 



5. Cyprimdce. Pseudobranchife, when present, glandular. Margin of the upper jaw formed by the 

 premaxillaries. Opercular pieces complete. Mouth toothless, teeth in lower pharyngeals. Head scaleless, 

 Ijody scaled or scaleless, never covered by osseous plates. Air-vessel present or absent. 



6. Ghipeidm. Pseudobranchia? usually well developed. Margin of the upper jaw formed by pre- 

 maxillaries and maxillaries. Opercular pieces complete. Abdomen usually keeled. No adipose dorsal. 

 Scales on body, none on head. Pyloric appendages numerous. 



7. Notoptei-idcB. PseudobrancliiiB absent. Margin of upper jaw formed by premaxillaries and 

 maxillaries. Opercular apparatus incomplete : a parieto-mastoid cavity on either side, leading into the 

 interior of the skull. A single rayed dorsal fin, a long anal. Head and body scaled. Two pyloric appendages. 



Family, I— SILUEID^E. 



Margin of the upper jaw formed mainly by the premaxillaries : the maxilla rudimentary, often 

 constituting the base of a barbel: no suh-opercle. Either the rayed or adipose dorsal fins may be 

 present or absent. Skin scaleless, and either smooth or covered with osseous plates, or scattered tubercles. 

 Air-vessel, when present, either free in the abdominal cavity or more or less enclosed in bone, it communicates 

 with the organs of hearing by means of the auditory bones. 



The Siluroid, or scaleless fishes, are popularly termed cat-fishes, due to their being provided with a 

 number of feelers or long barbels arranged around the mouth. They mostly prefer muddy to clear water, and 

 the more developed the barbels, the more these fishes appear to be adapted for an inland and muddy 

 fresh- water residence. 



The wider and deeper the rivers the more suited they are for the Siluridm, consequently the larger 

 forms are comparatively rare in the south of India, whilst they abound in the Indus, Jumna, Ganges, Irrawaddi 

 and other Burmese i-ivcrs. 



Due to their usual resort, these fishes appear to employ their feelers in moving about in muddy places, 

 and consequently have less use for their eyes than forms that reside in clear pieces of water. Thus it is, that 

 the size of the eye as compared with the length of the head is much great.n- in the young than in the adult. 

 The eye in fact atrophies, it does not increase in size in proportion with the remainder of the head, consequently 

 the length of the specimen must be taken into consideration. Some of these fishes have the skin of the head 

 passing over the eye without any trace of a free orbital margin, but this again may at times be due to age, 

 thus in the young of Macrones chryseus we find no free orbital margin, but one is distinctly present m the 

 adult. 



