692 
SCANDINAVIAN FISHES. 
tic bones, which are attached to the anterior end of 
the air-bladder. Several circumstances, of which we 
shall give an account below, seem, however, to assign to 
the Weberian apparatus its most important function as 
a barometrical apparatus for the fish. As in the File- 
fishes, we sometimes find here that the air-bladder is 
connected with the skin in the scapular region on each 
side of the bod}- ; and this is effected either immediately, 
lay means of lateral processes from the bladder, or by 
a ligamentous connexion between the skin or the first 
lateral plate and the acoustic bone that coalesces with 
the air-bladder. 
In the same parts of the body, the sides of the 
scapular region behind the clavicles, we find in some 
Glanomorphs ( Plotosus , MaJapterunis") special cavities, 
one on each side of the bod} 7 , more or less completely 
closed bulbs of the abdominal cavity (secondary abdo- 
minal cavities), in which a part of the liver and (on the 
right side) the gall-bladder or a portion of the kidneys 
may find room. In several Glanomorphs {Doras, Arias, 
Aspredo, Silurus etc.) we meet with a singular sac be- 
neath the skin behind each of the clavicles, usually 
opening into a hole ( poms lateralis 1. pectoralis ) at the 
upper angle of the pectoral fin, somewhat above or a 
little behind it. We have already remarked a similar 
cavity in the case of the Batrachoids (Part I, p. 133). 
It has been interpreted as a saccate poison-gland; but 
in neither case has its signification been yet explained. 
In our Sheatfish the pore leads upwards to the cavity 
under the flat, backward process from the posterior 
corner of the angular clavicle. 
These fishes are known in English as Catfishes on 
account of their long and sometimes numerous barbels, 
sensory threads (corresponding to whiskers) round the 
mouth. These barbels, accompanied sometimes by large 
labial flaps, are by their extraordinary development 
especially characteristic of the Glanomorphs. 
The variety of form among the Glanomorphs (Ne- 
matognates) is fairly great. About 660 species have 
been described, and Bleekee has distributed them among 
185 genera, arranged in 6 families. The form of the 
body varies from the ordinary piscine form, usually 
with flattened head and well-separated caudal fin, to the 
Anguilliform type, with the vertical fins continuous 
round the tip of the tail. The plated Glanomorphs, as 
Cope has remarked, present in their armour an obvious 
resemblance to the Sturgeons, to which the Glanomorphs 
possess another likeness in the barbels on the jaws. That 
the resemblance between these two groups of fishes is 
not merely external, has been already shown by Ban- 
ker 6 in his account of the analogy between the different 
parts of the scapular arch in the armoured Glanomorph 
Callichthys and in a Sturgeon, with posttemporale, supra- 
clavicula, clavicula and inter clavicula equally distinct as 
dermal growths. Thus the Glanomorphs — in the ma- 
jority of which, however, the structure of the scapular 
arch reminds us most strongly of the Carps — rank as 
the most distinct intermediate forms in this respect 
between the Sturgeons and the Teleosts. 
Most of the Glanomorphs belong to fresh water, 
especially to the lakes and rivers of the Tropics, with 
their deltas and brackish water; but many live in the 
sea, where they keep, however, to the littoral region. 
To the natives, especially within the Tropics, these fishes 
are in many localities of great economical value; but 
they are generally despised by Europeans on account of 
their repulsive appearance. Many of them too, especially 
in the tropical regions, are dreaded for their formidable 
spines, which are said to be poisonous, though as yet 
we have no trustworthy evidence on this head. 
Fam. SILURIDiE. 
Body naked {without plates on the sides); head also covered with skin. Only one {if any) dorsal fin furnished with rays, 
short and situated on the abdominal part of the body. Caudal part of the body and the anal fin long. Branchial 
arches simple {without appendicular branchice). Gill-openings large ; branchiostegal membranes free from the isthmus. 
Thus defined, the family of the Sheatfishes corre- 
sponds to Bleeker’s subfamilies Siluriformes and Ailice- 
formes — the former without, the latter with a small 
adipose fin on the posterior part of the dorsal margin 
a Cuv., Val., Hist. Nat. Poiss., vol. XV, pp. 415 and 525 a 
h Shoulder-girdle and Sternum (Ray Soc. 1867), p. 23. 
— as well as to his Saccobranchi formes, with their sin- 
gular, tubular, respiratory cavity along each side of 
the body, and contains about 50 known species from 
the Old World and the Sunda Islands. In Gunther 
1 Hyrtl, ]. C., p. 
302. 
