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uneven curvature is first of all to be removed, and the plate rendered perfectly flat.



86 TORTOISES AND TURTLES.

This is effected by immersing it in hot water, and then allowing it to cool under
heavy pressure between smooth blocks of wood, or metallic plates. The surface is
then rendered smooth, and the thickness equal, by scraping and tiling away the
rough and prominent parts. In this way each plate receives an equal and smooth
surface. But it is in many cases desirable to employ larger pieces than can be
obtained from single plates, and two pieces are then united together in the
following manner. The edges are bevelled off to the space of two or three lines,
and the margins, when placed together, overlap each other to that extent. They
are then pressed together by a metallic press^ and the whole is submitted to the
action of boiling water ; and by this means the two pieces are so admirably
soldered together as to leave no indication of the line of union. By the application
of heat, also, the tortoise-shell may be made to receive any impression by being
pressed between metallic moulds." Necklaces, etc., are made by pressing the
fragments and dust in moulds.

Turtles, more or less closely allied to the existing kinds, abound
Extinct Turtles.

in marine strata of the Tertiary and Cretaceous epochs, some belong-
ing to extinct and others to the living genera. Among the latter, the gigantic
Hoffmann's turtle (Ckelone hqfmanni), from the chalk of Holland, appears
to have been allied to the hawksbill, but had a shell of some 5 feet in length.
Extinct loggerheads occur in the .London Clay; and an allied extinct genus
(Lytoloma), common to the same formation and the upper Cretaceous deposits, was
remarkable for the great length of the bony union between the two branches of
the lower jaw, and also for the circumstance that the aperture of the internal
nostrils was placed right at the hinder extremity of the palate, as in crocodiles.
In strata older than the Chalk, such as the Purbeck and other Oolitic rocks, we
meet with turtles having heart-shaped shells, but clawed limbs, and a vacuity in
the centre of the plastron, these forming an extinct family (Acickelyidce), from
which the modern turtles have probably originated.

LEATHERY TURTLES.
Family DERMOCHEL YID^:.

The remarkable leathery turtle, or luth (Dermochelys coriacea), which is the
solitary survivor of a series of extinct forms, is one of those animals whose serial
position is a matter of dispute among naturalists ; some of whom regard it as so
different from all other Chelonians, that it ought to represent a suborder by itself,
while others believe it to be merely a highly specialised form allied to the true
turtles. From the evidence afforded by extinct species, the latter view, to our
thinking, appears the more likely to be the true one. The essential peculiarity of
the leathery turtle is to be found in the nature of its carapace, which is a mosaic-
like structure composed of a number of irregular discs of bone closely joined
together, and entirely free from the backbone and ribs. In certain extinct forms
the carapace, on the other hand, is represented merely by a row of marginal bones ;
from which it is inferred that these reptiles have been derived from true turtles by
a gradual disintegration and breaking up of the carapace. In the living genus the



TURTLES. 87

carapace is completely bony, and marked by seven prominent longitudinal keels ;
but the plastron is much less fully ossified, and carries five similar keels, the
unpaired entoplastral bone being wanting. The head, which is covered with small
shields, is remarkable for its relatively large size and globose form; the beak
having two triangular cusps situated between three deep notches. The jaws differ
From those of the true turtles in being sharp-edged from end to end, without any
expanded bony palate ; and there is also an important difference in the structure
oi' the skull itself, which may, however, be apparently the result of specialisation.
As in the true turtles, the limbs are converted into flattened paddles, which are,




Hat. size).



however, completely destitute of claws ; the front pair being much elongated,
narrow, and pointed, while the hinder ones are short and truncated. The humerus,
or hone of the upper arm, has the same general form as in the true turtles; and is
thus very unlike the corresponding bone of other members of the order. The
process marked h in the figure on p. 88 is more developed than in the turtles ;
and the Foramen e at the lower end is unique in the order. Largest of living turtles,
the leathery turtle exceeds 6 feet in length; and while in the young the front
flippers are equal in length to the shell, in the adult they become shorter. The
general colour is dark brown, which may be either uniform, or relieved with
yellow spots; the longitudinal tuberculated keels on the shell, as well as the
margins of the limbs, being invariably yellow in the young.



88



TORTOISES AND TURTLES.



This turtle is generally distributed throughout the tropical portions of the
Atlantic, Indian, and Pacific Oceans, from whence it occasionally wanders to the
consts of cooler regions. Yearly becoming scarcer, it is, however, one of those
species which stand a fair chance of extermination at no very distant date.
Although but little is known as to the mode of life of this turtle, it appears that
its food is chiefly of an animal nature, comprising fish, crustaceans, and molluscs.
In the breeding-season it appears in numbers on the Tortugas Islands, off the coast

of Florida, and sometimes in still greater abundance on
the sandy shores of Brazil. Arriving somewhat later than
the true turtles, it deposits its eggs in a similar manner,
laying as many as three hundred and fifty, in two batches ;
while at times, when three or more females have a nest in
common, upwards of a thousand eggs may be found in
a single spot. When hatched, the young turtles immedi-
ately seek the water, where, however, they have almost
as many foes as on land; so that it is probable only a
very small percentage arrive at maturity. The strength
and weight of a full-grown individual are very great; out-
captured some years ago, on the coast of Tenasserim,
requiring the combined efforts of ten or twelve men to
drag it on to the beach. The flesh has an unpleasant
flavour, and is not, therefore, generally eaten %

Gigantic as is the existing leathery turtle, it was
considerably exceeded by some of its extinct allies.
Among these, the huge Eosplmryis, from the London Clay,
with a skull of nearly a foot in length, apparently had a

carapace consisting only of one median row of broad-keeled bony plates, and a
border of marginal bones; while in Psephopkorus, from the higher Eocene and
Miocene strata of the Continent, both upper and lower shells were formed of
mosaic-like bones, which, it is thought, were overlain by horny shields. In the
earlier Protostega and Protosphargis, from the Cretaceous rocks of North America
and Europe, the upper shell appears to have been represented merely by a row of
marginal bones, while the lower one was very stoutly ossified ; some of these early
forms probably attained a length of from 10 to 12 feet.




FRONT VIEW OF LEFT HUMERUS
OF AN EXTINCT LEATHERY
TURTLE.



THE SIDE-NECKED TORTOISES.

Families ClIELYIDJE and

In place of withdrawing the head into the shell by means of an S-like
flexure of the neck in a vertical plane, as in all the groups hitherto described,
the remainder of the living tortoises with complete shells bend the neck side-
ways in a horizontal plane (as shown in the illustration on p. 92), and thus
bring the head within the margins of the shell. Accordingly, the group is
collectively spoken of as the side-necked tortoises, or Pleurodira. This character
is alone amply sufficient to separate the group from the foregoing assemblage



SIDE-NECKED TORTOISES.



89



of S-necked or Cryptodiran tortoises, but since there are also certain features
by which the skulls and shells of the two groups can be identified, it is im-
portant that these should be noticed. As regards the skull, this is distinguished
in the first place by the tympanic ring surrounding the aperture of the ear being
complete, as may be seen by comparing the accompanying figure with the one on
p. 47, and also by the circumstance that the lower jaw articulates by means of a






LOWER AND SIDE VIEWS OP SKULL AND UPPER AND LOWER ASPECTS OF LOWER JAW OP

GREAVED TORTOISE. (From Gray, Proc. Zool. Soc., 1870.,

:nob-like condyle with a corresponding cavity in the quadrate-bone, whereas in the
preceding group the positions of the condyle and cup are reversed. The shell,
which is always fully developed and forms a solid box, presents the peculiarity that
both the carapace and the hinder
part of the plastron are immovably
welded to the bones of the pelvis;
its upper and lower moieties thus
having a bond of union which is
totally lacking among the S-necked
tortoises. Further, the vertebrae of
the neck are furnished with pro-
jecting lateral or transverse pro-
cesses, which are absent from the
latter group.

In addition to these absolutely
characteristic features, there are cer-
tain other points connected with the anatomy of the side-necked tortoises which
demand a brief notice. With the exception of one species, which lacks horny




FRONT PORTION OF THE PLASTRON OF A SIDE -NECKED
TORTOISE, WITH THE HORNY SHIELDS REMOVED.

The thick lines indicate the boundaries of the shields.



TORTOISES AND TURTLES.



shields on the shell, the whole of these tortoises are characterised by the presence of

an intergular (i.gu) shield between the two gulars (gu) on the front of the plastron ;

such intergular shield being, as we have seen, but very rarely present in the

S-necked group. Very generally among the present assemblage one or more of the

pairs of costal bones of the carapace may meet in the middle line, owing to the

absence of some of the median unpaired series of

bones ; in certain cases the whole of the costals

thus meeting, owing to the absence of all the

neural bones. Whereas, in one family of the

group the plastron contains the same nine bones

as in the side -necked tortoises, in a second family

there are eleven bony elements in this part of

the shell, owing to the presence of an additional

(mesoplastral) pair between the normal hyo- and

hypo-plastral bones.

The side-necked tortoises, of which the great
majority may be included in the two families men-
tioned above, are all of fresh-water habits, and at
the present day are exclusively restricted to the
Southern Hemisphere, while they are the only
members of the order found in Australia and New
Guinea. During the earlier portion of the Tertiary
period they extended, however, into the Northern
Hemisphere, and in the preceding Secondary period
were abundantly represented in Europe. These

(.1,1,1 . HIGHT HALF OF THE CARAPACE OF THE

facts show that the group is a very ancient one :

J BLACK STEUNOTHKKE, WITH THE

and by the presence of the additional mesoplastral HORNY SHIELDS REMOVED.
elements in the lower half of the shell of some

of its representatives it is allied to a third and totally extinct group, which dis-
appeared before the close of the Secondary period.

Matamata The extraordinary reptile depicted in the accompanying illusti

Tortoise. tion, and known as the matamata (Chelys fimbriata), is the typie
representative of the first of the existing families of the group Chdt/ !<!'. Tl
various genera included therein are collectively characterised by having the normal
nine bones in the plastron, by the neck being incapable of complete retraction
within the margins of the shell, and the absence of a bony temporal arch to the
skull. Eight genera are included in the family, the range of which is restricted to
South America, Australia, and New Guinea.

The matamata, which is an American species inhabiting Guiana and North<-ni
Brazil, and is the sole representative of its genus, is easily recognised by its broad
and elongated neck, of which the sides are fringed with peculiar fimbriated pro-
jections, and the depressed and triangular head terminating in a proboscis-like
nose, and furnished with very small eyes. Not less characteristic is the equally
depressed and much corrugated shell, in which the carapace bears three longitudinal
ridges, subdivided into nodose protuberances by cross-valleys ; the horny shields of
the same being extremely rugose, and marked with deep radiating striae. The




SIDE-NECKED. TORTOISES.



vertebral shields are broader than long, and the hinder marginals are more or less
ngly serrated, while there is a distinct nuchal shield on the front edge of the
.rapace. On the removal of the horny shields from the carapace, it is seen that
only the last pair of costal bones meet in the middle line, owing to the presence of
but seven neural bones. The plastron is narrow and deeply notched behind, the tail
is very short, and the toes are fully webbed. In addition to the rows of fimbriated
ipendages on each side of the neck, there is a similar outgrowth of skin on the
in and larger pair of appendages above the ears. In colour the adult is uniform
, but the young are prettily marked with bands of brown and yellow on the




MATAMATA TORTOISE (\ nat. size).



chin and neck, while the shell is ornamented with black and yellow spots. The
species is of comparatively large size, the shell attaining a length of 15 inches.

Unfortunately, but little is known as to the mode of life of this strange tortoise.
When in its native element, the warty appendages on the neck float in the water
like some vegetable growth, while the rugged and bossed shell strongly resembles
a stone; and it is thus probable that the whole appearance of the creature is
advantageous either in deluding its enemies or in attracting to it the animals on
which it feeds the latter being the more likely hypothesis. Although it appears
that the matamata will occasionally eat vegetable substances, its chief food consists
of fish, frogs, and tadpoles, some of which may probably be attracted within reach



9 2



TORTOISES AND TURTLES.



by mistaking the appendages on the neck for plants or animals on which they feed.
The matamata is, however, stated to capture some of its prey by swimming swiftly
among water-plants, diving immediately that a fish or frog is seized in its beak.
In captivity this tortoise is sluggish, frequently dying after a few weeks through
refusal to feed.

Snake-Necked The snake-necked tortoises, of which there are two South American

Tortoises, species (Hydromedusa maximiliani and tectifera), agree with the

matamata in their long necks and weak jaws, but differ in their smooth shell, the

absence of a proboscis to the nose, and the presence of only four claws on ouch




SNAKE-NECKED TORTOISE (J Hat. size).



foot the matamata having h'vc claws on the fore-feet and four on the hinder pair.
The flattened shell in the young state has an interrupted median ridge, and presents
the unique peculiarity that the broad nuchal shield of the carapace is placed behind
the first pair of marginals (which consequently meet in the middle line), and thus
simulates a sixth vertebral shield. The figured species (H. tectifera), which ranges
from Southern Brazil to Buenos Aires, has a shell measuring about 8 inches in
length, and its feet largely webbed. In colour, the carapace is dark brown and the
plastron yellowish, with brown spots in the young; the head and neck being olive,
with a curved white streak on each side of the throat, and a broader white band,
edged with black, running along the sides of head and neck.



SIDE-NECKED TORTOISES.



93



Nocturnal and carnivorous in their habits, the snake-necked tortoises appear
to agree in their general mode of life with the majority of fresh- water species.
During the daytime they are generally to be found lying asleep on some dry spot
near the water, with the neck bent on one side, and the head, like the limbs and
tail, retracted within the margins of the carapace. When disturbed, the head and
neck are, however, shot out with marvellous rapidity, reminding the observer of the
sudden dart of a snake.

Australian Long - In Australia and New Guinea the place of the preceding group
Necked Tortoises. j s taken by another genus of long-necked tortoises, technically known
as Chelodina, the members of which may be recognised by the presence of a
normally placed nuchal shield
on the carapace, coupled with
the circumstance that the inter-
gular shield of the plastron,
instead of being placed between
the gulars, as in the figure on
p. 89, is situated behind the
latter, which consequently meet
in the middle line. The ver-
tebral horny shields are longer
than broad, and the whole of
the shields remarkable for their
extreme thinness. On remov-
ing the latter from the carapace,
it will be found that, owing to
the absence of neural bones
all the pairs of costal bones

et in the middle line, a peculiarity shared with one American, and two other
straliaii genera of the family. There are four species of these long-necked
tortoises, three of which are found in Australia, while the fourth is Papuan.

In addition to the foregoing, there are four other genera
belonging to the family under consideration, collectively distinguished
by their shorter necks, the length of which is inferior to that of the back. Of
these the American Rliinemys, Hydraspis, and Platemys are characterised by the
narrow anterior extremity of the lower jaw, and by the first vertebral shield of
the carapace being wider than either of the others. The second of these genera, of
which a member is represented in the accompanying figure, is by far the most
numerous in species ; and is noteworthy 011 account of being represented by a
fossil species in the Eocene deposits of India. The third genus differs from the
other two in the absence of neural bones to the carapace. On the other hand, the
two Australian genera Emydura and Elseya, both of which present the feature
last mentioned, are distinguished by the broad anterior extremity of the lower
jaw, and by the first vertebral shield of the carapace not exceeding the others
in size.

Greaved The tortoises which may be conveniently designated by a

Tortoises. translation of their scientific title (Podocnemis) so named on account




AN AMERICAN SIDE-NECKED TORTOISE



ther Genera.






94



TORTOISES AND TURTLES.



of the presence of a pair of large shields on the outer side of the hind-foot of the
typical species bring us to the second family of the group under consideration.
This family (Pelomedusidcv), which contains three genera, and is now confined to
Africa, Madagascar, and South America, is broadly distinguished from the last by
having eleven elements in the plastron, owing to the presence of a pair of nieso-
plastral bones ; while the neck is completely retractile within the margins of the
shell. The skull differs from that of the preceding family in having a bony
temporal arch, as shown in the figure on p. 89 ; while it lacks the distinct nasal
bones generally found in the former.

The largest and best known representative of the whole family is the giant
Amazonian tortoise (2 J odocnemis expansa}. which considerably exceeds in size all




GIANT AMAZONIAN TOUIOISE (J Hat. size).



other members of the entire group, having a shell which may measure as much MS
30 inches in length. It belongs to a genus including seven existing species, of
which six are South American, while the seventh is an inhabitant of Madagascar.
This extremely anomalous distribution is to some extent explained by the
occurrence of a fossil representative of the genus in the Eocene strata of India.,
which probably indicates that these tortoises were at one time widely spread. As
a genus, these tortoises are characterised by the skull having a roof over its
temporal region, coupled with the presence of five claws on the fore-feet, and four
on the hinder pair, and likewise by the circumstance that the mesoplastral bones
are small and confined to the edges of the plastron, .so that they are widely



SIDE-NECKED TORTOISES. 95

separated from one another in the middle line. The toes are broadly webbed, arid
the tail is remarkable for its extreme shortness.

The figured species, which inhabits tropical South America to the eastwards
of the Andes, and is extremely abundant in the upper part of the Amazonian
system, has the shell expanded posteriorly, and much depressed in the adult,
although at an earlier stage it has a roof-like form. The chin is furnished with
two small wart-like appendages ; and the hind-foot characterised by the presence
of two very large shields on its outer side. In colour, the upper shell is brown or
olive, with darker markings, while the plastron is yellowish, spotted with brown ;
the young being olive above and yellow beneath, with some yellow spots on the
head. All the other members of the genus are of greatly inferior dimensions; a
second Amazonian species (P. sextuberculata), having a shell of scarcely more than
a foot in length, and being distinguished from its larger relative by the presence
of only a single wattle on the chin.

The best account of the habits of these tortoises is the one given by Humboldt,
who speaks of the large species by its native name of arran. On the Orinoco,
according to this account, the period of egg-laying coincides with that of the
lowest level of the waters of the river, or from the end of January till the latter
part of March. During January the tortoises collect in troops, which soon leave
the water to bask on the warm banks of sand exposed by the lowering of the
river. Throughout February they may be found on such banks during the greater
part of the day ; but early in March the several troops collect in larger bodies, and
then make their way to the comparatively few islands where the eggs are
habitually deposited. At this -time, shortly before the egg-laying commences,
thousands of the tortoises may be seen arranged in long strings around the shores
of the islands in question, stretching out their necks, and holding their necks
above water, in order to see whether there is anything to prevent their landing in
safety. As the creatures are exceedingly timid, and especially averse to the
presence of human beings or boats, the Indians, to whom the harvest of tortoise-
eggs is of the utmost importance, take every precaution to prevent them being
disturbed, posting sentinels at intervals along the banks, and warning all passing
boats to keep in the middle of the river. When the tortoises have landed, the
laying of the eggs takes place at night, and begins soon after sunset ; the females
digging holes of some three feet in diameter and two feet in depth, by the aid of
their powerful hind-limbs. So great is the contention for space, that one tortoise
will frequently make use of a pit dug by a neighbour, and in which one set of eggs
has already been deposited, although not yet covered over with sand ; two layers
of eggs thus occupying one area. The crowding and jostling of the reptiles
necessarily leads to an immense number of eggs being broken, which is estimated
at a fifth of the whole ; the contents of the fractured shells in many places
cementing the loose sand into a coherent mass. The number of tortoises on the
shore during the night being so large, many of them are unable to complete the
work of egg-laying before dawn ; and these belated individuals become quite
insensible to danger, continuing there even in the presence of the Indians, who
repair to the spot at an early hour.

The great assemblage of these Chelonians takes place on one particular island



9 6 TORTOISES AND TURTLES.

in the Orinoco, hence known as the Boca de la Tortuga ; and according to native
accounts, no other spot is to be met with on the river from its mouth to its
junction with the Apure, where eggs can be found in abundance. On the island
in question, the number of eggs deposited is enormous; a large stretch of smooth
sandy beach being underlain with an almost continuous layer. To determine the
position and extent of the deposit, a long pole is thrust down at intervals into the
sand; the sudden want of resistance to its descent proclaiming when the L
layer containing the eggs has been reached. According to measurements taken l>y
Humboldt, the stratum extended to a distance of one hundred and twenty feet from
the water, and averaged three feet in depth. The whole is regularly parcelled out



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 11 of 62)