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Richard Lydekker.

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covered with rings of quadrangular shields. In si/e this tortoise is small, tin-
length of the carapace Iteing only about (i inches, and that of the tail some three-
quarters of an inch more. In the adult the colour is olive-brown above, and
yellowish brown beneath, but the young is more brilliantly coloured. Of the habits
and mode of life of this tortoise, nothing appears hitherto to have been ascertained.



MUD- TERRAPINS.



77



THE MUD-TERRAPINS AND THEIR ALLIES.

Families ClNOSTERNID^E and DERMATEMYDID^.

The mud-terrapins (Cinostemv/rri) bring us to tlie first of two nearly related
families confined to the New World, all of which differ from those previously
noticed by the circumstance that the nuchal bone of the carapace gives off from
each of its hinder angles a long rib-process which underlies the marginal bones.
From the second family, the mud-terrapins, of which there are eleven species
ibiting America north of the Equator, are broadly distinguished (as indeed they




v^~/v ^^~=r ^b^^^gL^^te >^gv C2_"" ^

PENNSYLVANIAN MUD-TEHRAPIN (| Hat. Size).

are from all other members of the order) by the fact that there are but eight bones
in the plastron, owing to the absence of the unpaired entoplastral bone. As
regards their other characters, the mud-tortoises resemble the Testudinidce in the
conformation of the vertebrae of the tail, and in the absence of a roof to the temporal
fossa of the skull, as well as in the extreme shortness of the tail. The carapace is
more or less depressed, and is articulated by a bony suture with the plastron ; the
latter having the gular shields fused into one, or wanting, and its fore and hind-
lobes more or less movable. The toes are fully webbed, and with the exception of
the fifth in the hind-foot, strongly clawed. The best known representative of the
genus is the Pennsylvania!! mud-terrapin (C. pennsylvanicum), which attains a
length of about 4| inches, and inhabits eastern North America from New York
to the Gulf of Mexico. In colour, the shell is brown or brownish above, and either
yellow or brown beneath, the lines of junction between all the shields being dark



78 TORTOISES AND TURTLES.

brown or blackish, while the head and neck are brown with yellowish spots.
From other species of the genus it i.s distinguished by the large size of the plastron,
in which the anterior lobe is narrower than the mouth of the shell.

In general habits the mud-terrapins seem to be very similar to the fresh-water
members of the tortoise family, although they prefer swamps and marshes to
running waters. Carnivorous in their diet, they subsist chiefly <>n small 1i-
insects, and worms, while they have been observed to capture newts. They will
readily take a baited hook, and when thus caught sink rapidly and heavily to the
bottom, thus causing the angler to believe that he has hooked a weighty fish. At
the commencement of winter they bury themselves in moss, where they remain
dormant till the following May. An extinct genus nearly allied to the mud-
tortoises occurs in the Tertiary rocks of Baden.

Maw's terrapin (Dermatemys mawi) may be taken as a good
representative of the second family, all the three genera of which are
restricted to Central America. This family connects the preceding one with the
snappers, agreeing with the latter in the presence of an entoplastral bone, and with
the former in the characters of the vertebrae of the short tail, which have the cup in
front, and the absence of a roof to the temporal fossa of the skull. Maw's terrapin
and its allies further agree with the mud-terrapins in the incompleteness of the
series of neural bones of the carapace ; the hinder ones being wanting, and thus
allowing the costal plates to meet in the middle line. Externally, the members of
the present family may be distinguished from the Testudinidce by the presence
of an additional series of infra-marginal shields between the marginals and those
of the plastron a feature which they possess in common with the big-headed
tortoise and the snappers. Maw's terrapin, which attains a length of some
15 inches, and is the sole representative of its genus, has the plastron large, and
connected with the carapace by an elongated bridge; the gular shield being single,
and the usual five other pairs of shields being present on the plastron. Unlike
most other tortoises, there are twelve pairs of marginal shields, in place of the
usual eleven. In the other two genera of the family Staurotypus and Claud if*
the plastron is reduced to a cross-like shape, and has but a short connection with
the carapace; while the number of paired shields on the former is only four or
or three, and the chin is provided with a pair of wattle-like appendages, of which
there is no trace in Maw's terrapin. While in the two species of Staurotypus tho<
plastron is connected with the carapace by a bony bridge, in the single represen-
tative of Claudius the junction is entirely ligamentous. This family is represented
by several extinct genera in the Tertiary and Cretaceous strata of North America.
one of which (Baptemys) had the full series of neural bones; and there appear i
to have been allied forms in the European Tertiaries.

THE SNAPPERS AND ALLIGATOR-TERRAPINS.
Family CHELYVRIDsE.

Resembling the big-headed tortoise in the great relative size of their hook-
beaked heads, and their elongate* 1 scaly tails, the snappers and alligator-terrapins



SNAPPERS.



79



bf North and Central America constitute a well-marked family by themselves,
[n the first place, they differ from the species named in that the majority of the
vertebras of the tail have the articular cup behind, and the ball in front ; while the
temporal region of the skull is but partially covered with a bony roof. The
American forms are further characterised by the relatively small size of the
2arapace, of which the hinder border is strongly serrated ; while the cruciform
plastron is likewise small, and but loosely articulated with the upper shell by a
very narrow bridge. Moreover, both the upper and lower shells are not completely
ossified till very late in life, vacuities remaining for a long time between




ALLIGATOR-TERRAPIN ( T ' 5 liat..size).



the costal and marginal bones in the former, and in the middle line of the
latter. Then, again, the plastron is peculiar in that the abdominal shields, which
are separated from the marginals by an inframarginal series, do not meet one
another in the middle line, although they may be connected by some small,
irregular, unpaired, additional shields. Further, the enormous head cannot be
completely retracted within the carapace, of which the anterior margin is deeply
excavated in order to afford it room ; and the chin is provided with one or more
pairs of pendent wattles. With the exception of the fifth in the hind-limb, the
toes are furnished with claws ; and the long tail is crested above.

Alligator- The alligator-terrapin, or snapping turtle (Chelydra serpentina)

Terrapin. j s a gi an t among river-tortoises, and takes its name from a fancied






8o TORTOISES AND TURTLES.

resemblance to an alligator surmounted by a chelonian shell. It is one of two
species belonging to a genus characterised by the eyes being directed upwards and
outwards, so that their sockets are visible in a top view of the skull ; by the tail
being furnished with large horny shields on its lower surface; as well as by the
absence of the supramarginal shields found on the carapace of Temmmck'g
snapper. The carapace, which may attain a length of at least 20 inches, is
characterised by its rugose surface, bearing three well-marked tuberculated keels,
which tend to become smoother with advancing age ; while its vertebral shields
are remarkable for their great width. The snout is short and pointed, with a very
narrow space between the 'eyes; the skin is warty, and on the chin is developed
into a pair of wattles or barbels. In the young the tail is as long or even longer
than the shell, becoming relatively shorter in the adult ; its upper surface having a
crest of large compressed tubercles, while the shields on the lower surface ha\i
been already alluded to. As in the other members of the family, the colour is a
uniform olive-brown. The alligator-terrapin inhabits the rivers of North America
to the eastward of the Rocky Mountains, from Canada to Mexico, and is also found
in Ecuador. A second living species (G. rossignonii), distinguished, among other
features, by the presence of four wattles on the chin, is met with in Guatemala
and Mexico. Nearly allied to this is a third and extinct species (C. murdti-
soni), from the Miocene rocks of Baden; and as we have already seen that the
mud-terrapins, and probably also Maw's terrapin, were represented in the Tertiary
strata of Europe, it is not improbable that the Eastern Hemisphere may have been
the original home of the present group of families.

Temminck's Attaining considerably larger dimensions than the alligator-
Snapper, terrapin, Temminck's snapper (Macroclemmys temmincki) is dis-
tinguished as a genus by the lateral position of the eyes, the sockets of which are
invisible in a front view of the skull, as well as by the presence of three or four
additional or supramarginal shields on the sides of the carapace, and by the under
surface of the tail being covered with small scales. The triangular head is pro-
portionately even larger than in the alligator-terrapin, and the carapace has three
very strongly marked longitudinal ridges. In length, the shell may measure at
least a couple of feet, the tail being somewhat shorter. This species inhabit.*-
North America from Western Texas to Florida, extending northwards to Missouri.
Since the alligator-terrapin and Temminck's snapper appear t<
be very similar in their mode of life, their habits may be treated of
collectively. Both these tortoises frequent alike the rivers and larger swamps of
the United States, occurring in certain localities in enormous numbers, and most
commonly in waters that have a muddy bottom, not even disdaining the most
malodorous pools. As a rule, they lie in deep water, near the middle of the river
or swamp, although at times they show themselves on the surface, where, with
outstretched neck, they will float with the current. In populated districts the
least sound is, however, sufficient to send them at once to the bottom, although in
more remote regions they are less shy. At times they may be observed at
considerable distances from the water, probably in search of food or of suitable
spots to deposit their eggs. Temminck's snapper well deserves its name, since.
from the moment of its escape from the egg, it commences to snap and bite at



TURTLES. 8 1

everything within its reach ; and an adult has been known to make a clean
perforation with its powerful beak through the blade of an oar half an inch in
thickness. When one of these tortoises is taken into a boat, Weinlaiid states that
it will rear itself up 011 its hind-legs, and with lightning-like speed throw itself
half a yard forwards to bite an oar ; and they have been known to inflict terrible
wounds on persons who have incautiously entered waters where they abound. In
the water the movements of these reptiles are more rapid than those of most of
their kin, and when in pursuit of prey they swim with surprising speed. Their
food consists largely of fish, frogs, and other water-animals ; while they will also
jquently seize and drag down large aquatic birds, more especially ducks and
iese. Tame specimens, that were kept in a pond in the United States, proved
3rrible foes to the stock of fish contained in the same. The eggs, which vary
>m twenty to thirty in number, and are about the size of those of a pigeon, are
leposited on the ground near the water, and are carefully covered over with leaves.
[11 captivity these tortoises thrive well in Europe, if the water be kept at a
sufficiently high temperature ; and a specimen of Temminck's snapper, which has
lived for more than thirteen years in the Brighton Aquarium, grew to a length of
3tweeii 4 and 5 feet from beak to tail, whereas, on its arrival, it measured less
laii a foot. In the confined limits of a tank the movements of this reptile were
^liberate and sluggish, and gave no idea of the activity characterising the wild
ite. Although the flesh of the adult of this species has such a strong musky
ivour as to be uneatable, that of the young is stated to be tender and palatable,
eggs are also sought after as articles of food ; and when two or three females
ive laid together, as many as from sixty to seventy may be taken from a
igle nest.

THE TURTLES.
Family GHELONID^E.

The families mentioned up to now have their feet more or less fully
lapted for walking on land, and the majority of the toes furnished with well-
'-veloped claws or nails ; while the carapace is generally of a somewhat oval
)rm. The true turtles, on the other hand, while agreeing with the foregoing in
iving their shells covered with horny plates, are at once distinguished by the
limbs being converted into flattened paddles, in which, at the most, only two of the
toes are furnished with claws. They are further characterised by the heart-like
form of the carapace, within which the head can be only partially withdrawn ;
while the plastron is never united by bone to the carapace, and vacuities remain
in the latter between the costal and marginal bones either throughout life, or for
a very long period. The skull has its temporal fossae completely roofed over by
bone ; and the vertebrae of the very short tail have the articular cup in front and
the ball behind. Entirely marine in their habits, and resorting to the shore only
for the purpose of breeding, turtles differ from tortoises and terrapins in that the
shells of their eggs are soft. In their entire conformation they are admirably
adapted for an aquatic life, the body being depressed to facilitate rapid progress
through the water, both the skull and shell being of unusually light and porous
VOL. v. 6



82



TORTOISES AND TURTLES.



Green Turtle.



structure ; while the limbs form most perfect paddles, capable of propelling the
animals with great speed. The head is placed upon the neck in such a manner as
to allow of the nostrils being readily raised above the surface of the water for tin-
purpose of breathing, and the nostrils themselves can be hermetically closed hy
means of a fleshy valve. The three best known species of turtles, which are
assigned to two genera; are inhabitants of all tropical and subtropical seas ; one
species the loggerhead occurring in the Mediterranean, and occasionally wander-
ing northwards.

Widely celebrated as being the source of the far-famed turtle-
soup of civic banquets, the green turtle (Cltelone 'my das} is one of two
species belonging to a genus characterised by the presence of four pairs of costal
shields on the carapace, and by the persistence of the vacuities between the costal

and marginal bones of the latter
throughout life. The plastron
is, moreover, distinguished 1>\-

o /

the presence of an intergular
shield between the two gulars ;
while, as in the second genus,
there is a row of inframarginal
shields between the marginals
and the proper shields of the
plastron. The skull is of moder-
ate size in comparison to the shell,
with the sockets of the eyes
placed nearly vertically, and
separated by a broad bar of
bone. Such are the characters
common to the two species of the
typical genus of the family.
The green turtle is specially
distinguished by its short beak,
which is devoid of a hook at the
tip, and by the shields of the
carapace being in contact by
their edges all through life. In

the young, the carapace shows a faint median keel ; while its hinder margin is at
most but feebly serrated at all ages. Generally there is but a single claw on each
paddle, although, in some instances, young specimens also have a claw on the
second digit. In colour, the shell of the adult is olive or brown, with yellowish
spots or marblings; while in the young it is uniform dark brown or olive above,
and yellow beneath, the limbs being bordered with yellow on the upper surface,
and inferiorly yellow with a brown spot near the extremity. The food of the
species consists of seaweeds, especially the seawrack, upon which the turtles
graze at the bottom o!' the water, rising occasionally to the surface to breathe.

Generally rejected as food, the hawksbill turtle (('. i n<l>r!c<it<i)
Hawksbill Turtle. .

enjoys thereby no respite from persecution, since it is eagerly hunted




GREEN TURTLE.



TURTLES. 8

for the beautifully mottled horny shields of its shell, which are the sole source of
the tortoise-shell of commerce. In its young state, the hawksbill may be readily
distinguished from the preceding species by the circumstance that the horny
shields on the back of the three-ridged shell overlap one another like the tiles on a
roof. With advancing age the shields gradually, however, become smooth, and in
very old specimens they meet at their edges, as in other members of the order.
At all ages the hinder margin of the carapace is more or less strongly serrated ;
and the compressed and sharply hooked beak will always serve to distinguish at a
glance a hawksbill from a green turtle. Moreover, the limbs always have two




HAWKSBILL TURTLES SWIMMING (J ff liat. size).

claws. In the adult, the shields of the carapace are beautifully marbled and
mottled with yellow and dark reddish brown, while the plastron is yellow, and the
shields on the head and paddles are brown with yellow margins. In size this
species is somewhat inferior to the green turtle, the carapace attaining a length of
about 32 inches, against 42 inches in the latter. In habits the hawksbill differs
markedly from the green turtle, being exclusively carnivorous.
Loggerhead The third, and probably the largest species of turtle, is the

loggerhead (Thalasvochelys caretta), easily recognised by its enormous
head and the presence of at least five costal shields on each side of the carapace,
which differs from that of the two preceding species by becoming completely
ossified in the adult state. The beak is strongly hooked ; and while in the young



8 4



TORTOISES AND TURTLES.



Habits.



there are usually two claws to each paddle, one of these frequently disappears in
the adult. In colour, the adult is brown above, and yellowish beneath ; but the
young is uniformly dark brown or blackish. The Mexican loggerhead (T. kern/'i \.
from the Gulf of Mexico, differs in having a median ridge on the bone of each jaw,
whereas in the ordinary species such ridges are confined to the investing horny
sheath. According to Mr. Gosse, loggerheads feed on cuttles and other molluscs,
their powerful beaks enabling them to crush strong conch-shells as easily as a man
can crack a nut.

Apart from the difference in their food, all turtles appear to be
similar in their general mode of life, never leaving the sea except l'< >r
the purpose of laying their eggs, and then shuffling along in an awkward, ungainly
manner. During the laying season they resort to low sandy coasts, especially
unfrequented tropical islands, in vast numbers ; and if once turned on their backs,

while on shore, are unable to
right themselves again. This
habit of resorting to the land
to lay their eggs clearly proves
it may be observed, the descent
of turtles from fresh -water
members of the order. Writing
of the green turtles at Aldabra,
one of the Seychelles group of
islands, Mr. Spurs remarks that
the males permanently frequent
the bay of that island, the
females when they attain full
maturity (twenty or twenty-
five years) disappearing alto-
gether. When the latter come
to the shore for the purpose of
laying, their shells are covered

with barnacles of two or three weeks' growth. Commercially, the females are
more valuable than the males, and, as they are more easily captured, the proportion
found on the island is one female to every ten males, although, for one of the
latter, about ten of the former sex are hatched. Turtles generally come ashore
on fine moonlight nights, displaying great caution in landing, and then generally
uttering a loud hissing noise w r hich serves to disperse many of their enemies. Once
landed, the female turtle, writes Audubon, " proceeds to form a hole in the sand,
which she effects by removing it from under her body with her hind-flippers,
scooping it out with so much dexterity that the sides seldom, if ever, fall in. The
sand is raised alternately with each flipper, as with a large ladle, until it has
accumulated behind her, when, supporting herself with her head and forepart on
the ground fronting her body, she, with a spring from each flipper, sends the sand
around, scattering it to the distance of several feet. In this manner the hole is due,
to the depth of eighteen inches, or sometimes more than two feet. This labour 1
have seen performed in the short space of nine minutes. The eggs are then




YOUNG LOGGERHEAD TURTLE.



TURTLES. 85

dropped one by one, and disposed in regular layers, to the number of one hundred
and fifty, or sometimes nearly two hundred. The whole time spent in this part
of the operation may be about twenty minutes. She now scrapes the loose sand
liack over the eggs, and so levels and smooths the surface that few persons on seeing
the. spot could imagine that anything had been done to it. This accomplished to
her mind, she retreats to the water with all possible despatch, leaving the hatching
of the eggs to the heat of the sand." During a season each female will lay three
clutches of eggs, at intervals of from a fortnight to three weeks, usually from one
hundred and twenty-five to one hundred and fifty in number. No sooner are the
young turtles hatched, than hosts fall victims to land-crabs, frigate-, and other sea-
birds, while, when they reach the sea, they are attacked by swarms of predaceous
fishes. To escape the latter, the young reptiles allow themselves to be carried out
by currents into deep water, where they are less readily seized. During the
breeding-season the males fight desperately with one another, to the great joy of
;the sharks, by whom the disabled ones are seized.

When first laid, the round eggs of turtles are never quite full, but before

I hatching become fully distended. In describing the breeding-habits of the turtles
kept in a pond near the dockyard in Ascension Island, Moseley states that in the
breeding-season the females dig great holes as large as themselves in a bank of
sand, in which to deposit their eggs. The sand in which the eggs are laid does not
feel warm to the hand, but during the daytime is rather cool, while it is at all
times moist. Its temperature appears to undergo no material variation, owing
to the depth at which the eggs are deposited ; such medium amount of heat being

S^icient for the hatching.
Although a largo number of green turtle are captured by being turned on
r backs while on shore, in the Seychelles and Bahamas they are harpooned.
Kneeling Island the method of capture is described by Darwin as follows :
e water is so clear and shallow that, although at first a turtle dives quickly
of sight, yet, in a canoe or boat under sail, the pursuers, after no long chase,
come up to it. A man, standing nearly in the bows at this moment, dashes
through the water upon the turtle's back, then, clinging with both hands to the
shell of the neck, he is carried away, till the animal becomes exhausted, and is
secured." In China and Mozambique turtles are captured by means of sucking-
fishes, which are taken to a spot where the reptiles are basking upon the surface
of the water. Each fish has a ring round its body to which a line is attached, and
as soon as it securely fastens itself by its sucking-disc to the back of a turtle, both
'Captor and captured are drawn ashore. Although those of the loggerhead have a
somewhat musky taste, the eggs of the other species of turtle are much esteemed
as articles of food, while all yield a valuable oil.

As already said, tortoise-shell is a product of the hawksbill turtle,
and it is too often taken from the back of the living animal by the
aid of heat, after which painful operation the unfortunate turtle is returned to its
native element. As the raw tortoise-shell is very unlike the finished article, with
which all are familiar, Bell's brief account of the process of manufacture may be
quoted. The horny shields, as removed from the turtle, being highly curved, " the



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 10 of 62)