140 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
Day (9) briefly refers to the air-bladder in what he then regarded as examples of 
two Indian species of this genus, viz., H. cenia, Ham. Buch., and H. viridescens, 
Ham. Buch., in the following terms: — “The air-vessel is placed transversely across 
the body of the anterior vertebra. It has an expanded globular portion on either side 
enclosed in a bony capsule, and with a transverse connecting tube.” This account 
is so greatly at variance with what we found in H. horneensis that we were not sur- 
prised to learn that Day (‘Proc. Zool. Soc.,’ 1876, p. 794) subsequently admitted 
that the specimens he examined were species of Gagata (= Callomystax). 
Ketengus typus. 
In this species also both the air-bladder and skeletal modifications are very similar 
to those of Arius pidada. 
Owing to the prominence of the sub-vertebral keel, and the extent to which the 
parallel ridges from the anterior, ventral, and posterior walls project inwards, the 
communication between the lateral halves of the anterior chamber is reduced to a 
relatively small and somewhat triangular foramen. Three j^airs of secondary trans- 
verse septa sub-divide the cavities of the two lateral compartments. 
A lateral view of the air-bladder with the outer wall of the right side removed, 
showing the dorsal ridge formed by the impression of the subvertebral keel (sv.k.), 
the parallel ridges (r.s.), and the foramen by which the lateral halves of the anterior 
chamber communicate with each other, is represented in fig. 50. In the same figure 
the primary and secondary transverse septa are also seen extending between the 
dorsal and ventral walls of the bladder {t.s., t.s.'). The lettering, a.p. and p.p. indi- 
cates the anterior and posterior pillars of the anterior chamber. 
yElurich thys longispinis. 
This Mexican Siluroid also bears a strong resemblance to Arius pidada. The 
walls of the air-bladder, however, are much thicker, and the dorso-lateral regions of 
the lateral compartments are strengthened internally by numerous column-like aggre- 
gations of vertically arranged fibres, separated by narrow slits, Avhich become less 
marked and finally disappear towards the anterior chamber. 
uElurichtliys Gronovii. 
Under the name of Galeichthys Gronovii, Cuviee and Valenciennes (8) briefly 
refer to the air-bladder of this species. The organ is said to be heart-shaped, broader 
in front than behind, emarginate anteriorly, and somewhat flattened. 
These writers also describe the bladder as possessing certain extrinsic muscles. 
'I’wo long, straight muscles are said to be connected with its dorsal surface, while its 
