Encyclopaedia Britannica > Volume 21, ROT-Siam

777
SHARK
to man; at least, there is no instance known of a person
having been attacked by the species common on the British
coast (Z. cornubica). It grows to a length of 10 feet, and
ranges to New Zealand and Japan. See vol. xix. p. 518.
To the genus Carcharodon particular interest is attached,
because the single still existing species is the most form¬
idable of all sharks, as were those which preceded it in
fertiary times. The existing species ((7. rondeletii) occurs
in almost all tropical and subtropical seas, but seems to be
verging towards extinction. It is known to attain to a
length of 40 feet. The tooth figured here of the natural
size (fig. 12) is taken from a jaw much shrunk in drying
but still 20 inches wide
in its transverse dia¬
meter, and taken from
a specimen 36£ feet
long. The extinct spe¬
cies must have been
still more gigantic in
bulk, as we may judge
from teeth which are
found in the crag or
which have been
dredged up from the
bottom of the Pacific
Ocean by the naturalists
of the “ Challenger ”
expedition, and which
are 4 inches wide at the
base and 5 inches long
measured along their
lateral margin. In FlG- 12-—Tooth of Carcharodon rondeletil
some Tertiary strata these teeth are extremely abundant, so
much so that—for instance, in Florida—the strata in which
they occur are quarried to obtain the fossil remains for ex¬
port to England, where they are con¬
verted into artificial manure.
The Fox-Shark or Thresher (A lopecias
vulpes), of which every year specimens
are captured on the British coast, but which is common
in all the temperate seas of the northern and southern
lemispheres, is readily recognized by its extremely slender
tad the length of which exceeds that of the remainder of
the body. Its teeth are small, flat, triangular, and without
serrature (fig. 13 ■ the single tooth is of the natural size).
It follows the shoals of herrings, pilchards, and sprats in
their migrations, destroying incredible numbers and fre-
quently injuring the nets by getting entangled in them.
When feeding it uses the long tail in splashing the surface
of the water, whilst it swims in gradually decreasing
circles round a shoal of fishes which are thus kept crowded
together, falling an easy prey to their enemy. Sometimes
two threshers may be seen working together. Statements
that it has been seen to attack whales and other large ceta¬
ceans rest upon erroneous observations; its dentition is
much too weak to bite through their skin, although, as
Couch says, by one splash of its tail on the water it may put
a herd of dolphins or porpoises to flight like so many hares,
ihe same effect may be produced by the splash of an oar.
The thresher attains to a length of 15 feet, the tail included.
The Basking Shark (Selache maxima), sometimes erro¬
neously called “Sun-Fish,” is the largest fish of the North
Atlantic, growing to a length of more than 30 feet. It is
one of the few types of sharks which up to a very recent
time were considered to be peculiar to the North-Atlantic
fauna; but Prof. F. M‘Coy has just recorded its occur¬
rence on the Australian coast, a specimen 30 feet long
having been captured in November 1883 at Portland, on
the. west coast of Victoria. The mouth is of an extra¬
ordinary width, and, like the gill-cavity, capable of great
expansion, so as to enable the fish to take at one gulp an
enoimous quantity of the small fish and other marine
ci eatuies on which it subsists. Also the gill-openings are
of great width. The teeth are very small, numerous,
arranged in several series, conical, and probably without
use in feeding. This shark is therefore quite harmless if
not attacked. On the west coast of Ireland, where it is
Fig. 13.—Basking Shark.
frequently seen during the summer months, generally in
companies, at a distance of from three to a hundred miles
off the shore, it is chased by the more courageous of the
fishermen for the sake of the oil which is extracted from
the liver, one fish yielding from a ton to a ton and a half.
Its capture is not unattended with danger, as one blow
from the enormously strong tail is sufficient to stave in
the sides of a large boat. The simple method used at
present of harpooning the fish entails much patience and
loss of time upon the captors, as the fish generally sinks to
the bottom and sulks for many hours before it rises again
in a more or less exhausted condition ; and the use of more
modern appliances could not fail of securing more speedy
and better success. The basking shark is gregarious,
and many individuals may be seen in calm weather lying
together motionless, with the upper part of the back raised
above the surface of the water, a habit which it has in
common with the true sun-fish (Orthagoriscus), and from
which it has derived its name.
A shark similar in many points to the basking shark
(which it exceeds in size), and an inhabitant of the Indo-
Pacific Ocean, is Rhinodon iypicus. In fact, so far as our
present knowledge goes, it is the largest of all sharks, as it
is known to exceed a length of 50 feet, but it is stated to
attain that of 70. The captures of only a few specimens
are on record, viz., one at the Cape of Good Hope, one or
two near the Seychelles, where it is known as the “chagrin,”
one on the coast of California, and one (quite recently) on
the coast of Peru. The snout is extremely short, broad,
and fiat, with the mouth and nostrils placed at its extrem¬
ity ; the gill-openings very wide, and the eye very small.
The teeth are, as in the basking shark, extremely small
and numerous, conical in shape. No opportunity should
be lost of obtaining exact information on this shark.
The Greenland Shark (L&margus borealis) belongs to the
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