ion of all Silurids, being represented in almost all
tropical countries which are drained by large rivers. Most of the
species live in salt water. They possess six barbels, and their head is
extensively osseous on its upper surface; their dorsal and pectoral
spines are generally developed into powerful weapons. _Bagarius_, one of
the largest Silurids of the rivers of India and Java, exceeding a length
of 6 ft., differs from _Arius_ in having eight barbels and the head
covered with skin.

R. Semon has made observations in Queensland on the habits of _Arius
australis_, which builds nests in the sandy bed of the Burnett river.
These nests consist of circular basin-like excavations about 20 in. in
diameter, at the bottom of which the eggs are laid and covered over by
several layers of large stones. In the marine and estuarine species of
_Arius, Galcichthys_ and _Osteogeniosus_, the male, more rarely the
female, carries the eggs in the mouth and pharynx; these eggs, few in
number, are remarkably large, measuring as much as 17 or 18 millimetres
in diameter in _Arius commusonii_, a fish 3 or 4 ft. in length.

The common North American _Amiurus nebulosus_ also takes care of its
eggs, which are deposited beneath protecting objects at the bottom of
the water, failing which both parents join in excavating a sort of nest
in the mud. The male watches over the eggs, and later leads the young in
great schools near the shore, seemingly caring for them as the hen for
her chickens.

[Illustration: FIG. 2.--_Synodonus xiphias_.]

In the _Siluridae Stenobranchiae_ of Gunther the dorsal fin consists of
an adipose portion and a short-rayed fin which belongs to the abdominal
vertebral column, and, like the adipose fin, may be sometimes absent.
The gill-membranes are confluent with the skin of the isthmus. The
Silurids belonging to this section are either South American or African.
Among the former we notice specially the genus _Doras_, which is
distinguished by having a series of bony scutes along the middle of the
side. The narrowness of their gill-openings appears to have developed in
them a habit which has excited the attention of all naturalists who have
visited the countries bordering upon the Atlantic rivers of tropical
America, viz. the habit of travelling during seasons of drought from a
piece of water about to dry up to ponds of greater capacity. These
journeys are occasionally of such a length that the fish have to travel
all ni