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among the Indians, who proceed to work the layer with the regularity of miners.
The earth having been removed, the eggs are carried in small baskets to the
neighbouring encampment, where they are thrown into long wooden troughs of
water. Here they are broken and stirred up with shovels, and the mass then left
in the sun till all the oily matter has collected at the surface, whence it is
continually ladled off, and taken off to be boiled over a quick fire. The result of
this process is a limpid, inodorous, and scarcely yellow substance, known as " turtle-
butter," which can be used for much the same purposes as olive-oil. In spite of
the enormous quantity of eggs thus taken, numbers are hatched, and Humboldt
saw the whole bank of the Orinoco swarming with small tortoises of an inch in
diameter, that escaped only with difficulty from the pursuit of the Indian children.
All these tortoises are vegetable feeders ; and the females greatly exceed the males in
size. On the upper Amazon the large species, according to Bates, is captured either
by means of nets or by shooting with arrows. On such occasions, after the net is
set in a semicircular form at one extremity of a pool, the rest of the party spread
themselves around the swamp at the opposite end, and begin to beat with poles in
order to drive the tortoises towards the middle. This process on the occasion
referred to "was continued for an hour or more, the beaters gradually drawing
nearer to each other, and driving the hosts of animals before them ; the number of
little snouts constantly popping above the surface of the water showing that all
was going on well. When they neared the net, the men moved more quickly.
shouting and beating with great vigour. The ends of the net were then sei/.ed l>y
several strong hands and dragged suddenly forwards, bringing them at the same
time together, so as to enclose all the booty in a circle. Every man now leapt into
the enclosure, the boats were brought up, and the turtles easily captured by thiJ
hand and tossed into them." Altogether, about eighty individuals were captured
in the course of twenty minutes or so. In shooting tortoises, the arrow employed
has a strong lancet-shaped steel point, fitted to a peg which enters the tip of the;
shaft. To the latter the peg is secured by a hank of twine some thirty or forty
yards in length, and neatly wound round the body of the arrow. When a tortoise
is struck, the peg drops out from the shaft, and is carried down by the diving
animal, leaving the latter floating on the surface. Thereupon the sportsman
paddles up to the arrow, and proceeds to " play" his victim until it can be drawi
near to the surface, when it is struck with a second arrow, after which, by the aio
of the t\vo cords, it can be safely drawn ashore. In many villages on the Amazon
every house has a pond, in which a number of these tortoises are kept for food.



SIDE-NECKED TORTOISES. 97

The other two genera of the family Pelomedusa and Sterno-
therus differ from the first by the absence of a bony roof to the
emporal region of the skull, and likewise by the presence of five claws in both the
Yont and hind-feet. Whereas, however, the former has the mesoplastral elements
>(' the plastron small and similar to those of the greaved tortoises, in the latter
hey are as well developed as the other elements of the plastron, meeting in the
niddle line.. Pelomedusa is represented by a single species common to Africa
aid Madagascar, but of the six species of Sternotherus, five are exclusively African,
vhile the sixth inhabits both Eastern Africa and Madagascar. The right half
if the upper shell of one of the species is represented on p. 90.

A remarkable Chelonian (Carettochelys insculpta} from the Fly

7 ly River Turtle. . . *

River, New Guinea, differs from all other members of the group, in

In- absence of horny shields on the shell and the conversion of the limbs into
Middles, each of which carries but two claws. The neck is not retractile. In the
a rapace there are six very small neural bones, which are not in contact with one
mother, thus allowing each pair of costals to meet in the middle line ; and the
olastron has only the usual nine bones. A wavy sculpture ornaments the whole of
;he external surface of the shell, which attains a length of about 18 inches. The
lead is large, and the tail relatively short. The species, which represents a
separate family (Car ettochely idee), is still very imperfectly known ; and it has
Deen suggested that it does not belong to this group at all. It is not improbable
hat a chelonian (Hemichelys), from the Eocene rocks of India, indicates a second
iH'inber of the same family, as its shell was similarly devoid of horny shields.
Australian Probably the most aberrant members of the whole order were

ed Tortoises, certain gigantic tortoises (Miolania) from the superficial deposits of

Australia, characterised by the presence of
several pairs of horn-like protuberances on the
skull, and also by the investment of the tail in
a bony sheath, recalling that of the armadillos.
Unfortunately, the shell of these strange reptiles
is known only by fragments; but, from the
conformation of the bones of the feet, we are

VIEW OK SKULL OF HOHNED TOUTOISE.

enabled to say that they were terrestrial, while

structure of the palate indicates that they were herbivorous. They clearly
institute a fourth family (Miolaniidce) of side-necked tortoises.
Extinct European The Secondary rocks of Europe contain the remains of a number
Genera. o f extinct tortoises which may be referred to a fifth family (Plesio-
"kelyidce) of the group. While agreeing with the existing Chelyidce in having but
nine bones in the plastron, these extinct forms differ by the much greater thickness
jf their shells, and also by the circumstance that only one of the lower bones of
the pelvis is welded to the upper surface of the plastron, whereas in the existing
families both are thus united. Abundant in both the Oolitic and Wealden rocks,
,the majority of these tortoises are referred to the genus Plesiochelys, although
some, as the one of which the carapace is represented in the figure on the next page,
are separated as HylcEchelys, being distinguished by the enormous width of the
vertebral shields, in which the breadth may be three times the length. Nothing
VOL. v. 7




TORTOISES AND TURTLES.



approaching this conformation is to be met with among living representatives of
the order.

Generalised Certain extinct tortoises, such as Pleurosternum from the

cneionians. Purbeck Oolite of Swanage, and Baena of the Eocene rocks of the

United States, indicate the existence of an extremely generalised group of the

order Amphichelydia, presenting many characters common to the existing

S-necked and Side -necked
groups, and which may have
been the ancestral stock of
both the latter. All have
eleven bones in the plastron,
owing to the presence of
mesoplastrals, and an inter-
gular shield, but the pelvis
may or may not be connected
with the plastron. In the
first of the genera named,
the mesoplastral bones extend
right across the shell to meet
in the middle line, and one
of the bones of the pelvis
articulates to a smooth oval
facet on the plastron. On
the other hand, in the second
genus, the mesoplastral bones
are incomplete, as in the
existing greaved tortoises,
and there is no union between the pelvis and the plastron. Since it is probable
that the plastron of the Chelonians has originated from a system of abdominal
ribs similar to those of the tuateras (Chapter VI.), it is interesting to notice that
these generalised tortoises had a larger number of plastral elements than are to
be found in the majority of the existing representatives of the order.




IMPERFECT CARAPACE OF WIDE-SHIELDED WEALDEN TORTOISE.



THE SOFT-TORTOISES.
Family TRIONYCHID^E.

The last group of the order comprises the soft river-tortoises, now confined to
the warmer regions of Asia, Africa, and North America, but which, during the
middle portion of the Tertiary period, appear to have been extremely abundant in
the rivers of England and other parts of Europe. The whole of these tortoises are <
included in a single family which forms a group of equivalent value to the S-necked
and Side-necked sections ; and it is not a little remarkable that while in the
greater part of their organisation they approximate to the former group, in certain
features connected with the skull they come nearer to the latter. The most
striking peculiarity of the soft-tortoises is to be found in the nature of their shells,




w










SOFT RIVER TORTOISES



SOFT- TORTOISES. 99

which are covered with a raised sculpture of variable form, and are quite devoid of
horny shields. The lower shell, or plastron, is always very imperfectly ossified,
and completely separate from the carapace ; while the carapace never has a complete
series of marginal bones, and passes at its borders into a soft expansion of skin,
from which the name of the group is derived. If marginal bones occur at all,
they are confined to the hinder border of the shell, and are unconnected with the
ribs ; having, in fact, nothing in common with the bones so named in other tortoises,
and being doubtless of independent origin. In being unconnected with the plastron,
the pelvis resembles that of the S-necked group, and the head is retracted by a
similar S-like flexure of the neck in a vertical plane. In regard to the mode of
articulation of the lower jaw with the skull, and likewise in the presence of a
notch in the hinder border of its tympanic ring, the soft-tortoises again resemble
the group last mentioned ; although in the general form of the skull and the
conformation of the palate they come nearer to the Side-necked group. A distinc-
tive peculiarity of the skeleton is to be found in the presence of at least four joints
in the fourth toe of each foot. Externally, the soft-tortoises are characterised by
their long necks, which, together with the head, can be completely withdrawn into
the shell, and also by the proboscis-like snout, and the thick fleshy lips concealing
the jaws. The ear is completely concealed ; and each foot, as indicated by the
scientific name of the group, has but three claws, which are borne by the three
inner toes. As a rule, the colour of the skin is greenish olive, with yellow or
orange spots, passing into streaks on the under surface of the head ; while some
Decies have a few much larger eye-like spots on the back of the shell.

Although the whole of the soft-tortoises are included in a single
Typical Genus. , ., ,, ,..,.,. ,, ,. , . ,

family, they are arranged in six distinct genera, three or which are

learly allied to one another, as are likewise the remaining three among themselves.
The first and largest genus, Trionyx, contains fifteen living species, with a distribu-
ion coextensive with that of the family. These are characterised by the absence
)f a fold of skin on the hinder part of the under shell, beneath which the leg may
concealed, by the sculpture on the shell being generally in the form of wavy
raised lines, and by the hyo- and hypoplastral bones of the lower shell remaining
listinct from one another. In the skull, as shown in the figure on p. 89, the

)ckets of the eyes are placed relatively far back, and widely separated from the
iperture of the nose. Among the better-known species we may mention the
Jangetic soft-tortoise (T. gangeticus), now confined to the river system from which
takes its name, but formerly found, as shown by fossil specimens, in the

Tarbada; the length of the shell and fleshy disc reaching as much as 2 feet,
all the Old World representatives of the genus, this species has eight pairs of

)stal bones in the carapace; while it belongs to a subgroup characterised by
laving two neural bones between the first pair of costals, and by the absence of a
)ronounced ridge in the middle of the upper surface of the extremity of the lower
jaw. The soft-tortoise of the Nile (T. triunguis), ranging over Africa and Syria,
and attaining still larger dimensions, belongs to a second subgroup, distinguished
by having only a single neural bone between the first costals ; while Phayre's soft-
tortoise (T. phayrei), of Burma, may be taken to represent a third section differing
from the last by the presence of a median ridge in the front of the lower jaw. On



TOO



TORTOISES AND TURTLES.



the other hand, all the American soft-tortoises, of which T. fcro.r. is a well-known
example, differ by having only seven pairs of costal bones. Numerous representa-
tives of the genus occur in the Miocene and Eocene strata of Europe, as well as
in the Tertiary rocks of India and the United States. Two other members of

the iirst subfamily, confined to Asia,
represent as many genera. Of these
Cantor's soft-tortoise (Peloclielys cflMM
tori), from India, Burma, and Malay ana,
has the sockets of the eyes placed
more anteriorly than in the type genus.
This forward position of the eye-sockets
is still more marked in the much elon-
gated skull of the great Indian chitra
(Ghitra indica), where they are placed
close up to the nose.
Granulated soft- The three remaining
Tortoises. genera of the family are
characterised by the sculpture of the
shell generally taking the form of small
pustules, and thus resembling shagreen ;
while the hyo- and hypoplastral bones
of the lower shell are united ; and there
is a flap of skin on each side of the under
surface, beneath which the hind-limbs
can be concealed. All the forms art-
confined to the Old World ; and while

one of the three genera is Indian, the other two are African. The Indian genus
Emyda is readily characterised by the presence of a complete series of neural
bones in the carapace, coupled with a semicircle of marginal bones at its him lei-
extremity. In neither of the three living species does the length of the shell and
its soft disc exceed 10 inches, but much larger fossil forms are found in tl it-
Pliocene rocks of India. Both the African genera lack marginal bones, but whereas
in one (Cycloderma) there is a full series of neural bones to the carapace, in
the other (Cyclanarbis) these form an incomplete and interrupted series.

All the soft-tortoises are thoroughly aquatic, most of them but
rarely leaving the water except for the purpose of laying their eggs,
and in consequence of these habits very little is known as to their mode of life.
Although confined as a rule to rivers, a few of the species frequent estuaries, and
Cantor's soft-tortoise has been found some distance out at sea. Occasionally,
again, specimens of the Indian granulated soft- tortoises have been met with
wandering on land far from the neighbourhood of water. Fiercer and more
spiteful than any other members of the Chelonian order, these tortoises, owing to
a peculiarity in the structure and mode of articulation of some of the vertebrae of
tin- neck, have the power of darting out the head with inconceivable rapidity,
111'' great Indian chitra being facile princepn in this respect. Owing to this habit
tin- larger species are dangerous creatures to approach incautiously, as tin -ir l>it<-




CANTOR'S SOFT-TORTOISE.



Habits.



FLESIOSAURS. 101

is very severe ; and the natives are not unfrequently bitten by them in India and
Burma whilst bathing. All the members of the typical genus, together with
Cantor's soft-tortoise and the chitra, are known to be carnivorous, and it is
commonly believed that the same is the case with the other members of the group.
According, however, to Dr. J. Anderson, this is incorrect with regard to the
granulated soft-tortoises of India, which he expressly states to be exclusively
vegetable and grain -feeders. The larger species probably feed both on fish and
other aquatic animals, and on the flesh of such carcases as may be floating in the
rivers they inhabit. In correlation with their asserted herbivorous habits,
the small granulated species do not snap and bite after the manner of their
arger cousins. On shore, according to the observer last mentioned, when left to
.emselves, these species will slowly and cautiously extend their necks, and when
approached, instead of attempting to escape, withdraw rapidly into their shells,
of which the upper and lower anterior margins then meet. It is stated that all
the species are chiefly nocturnal, remaining during the daytime partially or
completely buried in the mud at the bottom of the water, and not beginning
to swim till sundown. Such species as inhabit marshes or swamps, liable to
be dried up during the hot season, bury themselves in the mud, at no great
depth below the surface, during the period of drought. As these tortoises
are known to remain frequently for a period of from two to ten hours, and
occasionally as much as fifteen hours, beneath the water, without coming to

surface to breathe, it is obvious that they must have some special means of
/genating their blood. It is probable, indeed, that certain filamentous
appendages of the mucous membrane of the throat found in these tortoises
subserve the office of gills, and thus enable the blood to be renovated by means
of the atmospheric air dissolved in the water they inhabit. With regard to
.eir breeding-habits, it appears that the females of the granular shelled species
ape a shallow hole in the mud, in which the eggs are laid and then carefully
ivered up, the eggs themselves being round, and about an inch in diameter.

THE PLESIOSAURS OR LONG-NECKED MARINE LIZARDS.
Order SAUROPTERYGIA.

Strikingly different in appearance as are the skeletons of the members of the
o groups, it appears that, on the whole, the nearest allies of the tortoises and
urtles are those extinct reptiles known as plesiosaurs, or long-necked marine
lizards, whose range in time embraced the whole of the great Secondary period,
during which were deposited the vast series of strata extending from the Chalk
downwards through the Oolites to the Lias and Trias. These reptiles agree with
the tortoises in that all or nearly all of the ribs of the back are articulated to the
vertebrae by single heads, and in the absence of hook-like (uncinate) processes to
the ribs, as well as in the want of a breast-bone or sternum. In the skull the
quadrate-bone is immovably fixed, and the palate more or less completely closed.
Both groups have the lower bones of the pelvis expanded into large flat plates,
and there is also a similarity in the structure of the bones of the limbs.

Whereas, however, the tortoises have the upper surface of the body covered






102



PLESIOSAURS.



\vith ;i shell, and the lower aspect of the same protected by a plastron, the
plesiosaurs were entirely naked, the plastron being represented by a numerous
series of abdominal ribs, each composed of three pieces, forming a forwardly-
directed angle. The skull differs from that of the crocodiles in having but one
(lower) temporal arch; and the jaws are furnished with a number of pointed and
grooved teeth, implanted in distinct sockets; one of such teeth being figured
on p. 5. The neck was generally much elongated, and its vertebrae differ from
those of crocodiles in that their ribs which may have either single or double




RESTORED SKELETON OF A FLESIOSAUR (greatly reduced).

heads, are articulated only to the body of each vertebra (as shown in the accom-
panying figure); those of crocodiles always having two heads, of which the
lower is articulated to the body, and the upper to the arch of the vertebra.
Throughout the backbone the bodies of the vertebrae have either nearly flat or
slightly cupped articular surfaces ; and in the region of the back each pair of ribs
is articulated to a process arising from the arch of each vertebra, instead of
from a facet placed at the junction of two vertebrae, as in the tortoises. Although
there are other interesting features in these reptiles, those mentioned distinguish

them from crocodiles and dinosaurs on
the one hand, and tortoises and turtles
on the other.

With regard to the various groups
into which the order is divided, it ma\
be mentioned that in the typical forn
constituting the family Plcsiosauru
the limbs, as shown in the figure on p. II
are converted into flattened paddles, wit
a shortening of the bones 'of the upj
segments, and an increase in the numl
of bones corresponding with those of tl
toes of ordinary reptiles. In the ti
plesiosaurs (Pleaiosaurus) of the Lias,

ribs of the iii-ck were articulated to the vertebra' by two heads: whereas, in tl
later cimoliosaurs (Cimoliosaurus) of the Oolites and Chalk, such ribs, as shown ii
the figure of a neck -vertebra, were single-headed. Some of these creatures wi
of huge si/e, attaining a length of between Jit) and 40 feet; certain of the specie




UPPER SURFACE OF THE SKDLL OF T1IK siMiiSAMi,
OR THIASSIC PLESIOSAUR.

n, nostrils ; or, eye-sockets ; st, temporal fosse
(i nat. size). From (Jaudry.



PLESIOSA URS.



103



from the Cretaceous strata having a neck much exceeding the body and tail in
length, and containing as many as forty vertebrae. Marine and carnivorous in
their habits, these formidable creatures probably lurked in shoal-water, from
whence they darted their long necks to seize passing fishes in their jaws.
In the groups mentioned the head was comparatively small, but in the huge
pliosaurs (Pliosaurus) of the upper Oolitic strata the skull was of enormous
size, attaining in some instances a length of 6 feet, and the neck proportionately
short and thick. Their
teeth had more or less
triangular crowns, and
in some cases, inclusive
of the root, measured
quite a foot in length.
As is the case
with ail the higher
aquatic Vertebrates,
there is evidence to
show that the plesio-
saurs were originally
.erived from land
imals ; the repre-
ntatives of the
>up found in the
earlier (Triassic)
Secondary rocks hav-
ing limbs departing
much less widely from
ordinary type,

id bearing claws at the extremities of their digits. In the small lariosaur, which
leasured about a yard in length, the limbs appear to have been somewhat
itermediate in structure between the clawless paddles of the true plesiosaurs
and those of more ordinary reptiles; and the creatures were probably amphibious
in their habits, spending part of their time on land, and part in the water. In the
allied nothosaurs and simosaurs the limbs were better adapted for walking, from
which we may infer that their owners were still more terrestrial in their habits.





FRONT AND SIDE-VIEWS OF A NECK-VERTEBRA OF A PLESIOSAURIAN.

pr.z, and pt.z, anterior and posterior articular surfaces of the arch ; co, rib.




Ul'l'ER ASPECT OF THE SKELETON OF THE LARIOSAUR, A SMALL PLESIOSAURJAN.



CHAPTER IV.

SCALED REPTILES LIZARDS AND CHAMELEONS, Order SQUAMATA ;
Suborders LACERTILIA AND RHIPTOGLOSSA.

ALTHOUGH in popular language the term lizard is applied to any four-legged reptile,
exclusive of turtles and crocodiles, in scientific usage it is more convenient to restrict
it to those members of the great group of scaled reptiles which do not come under
the designation of either chamaeleons or serpents, whether they are provided with
legs, or whether they lack those useful appendages. Formerly, indeed, lizards and
chamseleons were regarded as constituting an order by themselves quite apart from
serpents, but the two groups are now known to be so intimately connected as to
render any such division inadmissible ; and they are accordingly here placed in a
single order, known as scaled reptiles, or, technically, Squamata. Structurally, this
ordinal group differs very widely indeed from any of those hitherto treated, and as
it is essential to gain a correct idea of such structural differences, they may first be
taken into consideration.

Taking their name from the coat of overlapping horny scales

with which they are generally invested, the scaled reptiles are

primarily distinguished from all the foregoing groups by the circumstance that the

quadrate-bone is more or less inovably articulated to the skull, and has its lower

end projecting freely therefrom, instead of being immov-
ably wedged in among the other bones. To this primary
point of distinction it may be added that the lower
temporal arch of the skull is wanting, so that there is
no bony bar connecting the lower end of the quadrate-
bone with the upper jaw, as there is in the crocodiles ;
the absence of this bar being well shown in the figure of
a lizard's skeleton. Then, again, the palate, instead of
being more or less completely roofed over by bone, is



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 12 of 62)