Chapter XVII: Part II: Reptilia (5)

In young specimens, under one foot in length, each of the neural and costal shields is strongly keeled, the three rows of keels converging towards the posterior end of the shell. The neural series of keels is almost continuous, and remains longest, even in half-grown specimens. The twelve pairs of marginal shields form at first a strongly serrated sharp edge; the serrations disappear gradually on the front portion, but remain on the posterior half of the shell. The horny covers of the jaws form a hooked beak, with sharp but smooth or feebly denticulated margins. The fore- and hind-flippers have two claws. The young are pale brown above, blackish below; the shell of the adult is beautifully marbled with yellow on a rich dark-brown ground; the plastron is yellow. The shields and scales of the head and limbs are dark brown, with yellow margins. The top of the head is covered by a large unpaired frontal and a pair of prefrontal or interorbital shields. This Turtle does not reach the size of the green or edible kind; the largest shell on record is in the National Collection, and measures 85 cm. = 34 inches in length. They range over all the tropical and subtropical seas. They are apparently strictly {386}carnivorous, living upon fish and molluscs, the shells of which they crunch. Although not eaten, they are much persecuted on account of their shells, the horny shields of which are the "tortoiseshell" of commerce. A large specimen yields up to 8 lbs. Few of the shields are, however, thick enough to be manufactured into the larger articles which art and fashion delight in, but if heated in oil, or boiled, they can be welded together under pressure, and be given any desired shape. In genuine articles of Oriental manufacture these welds can generally be detected, or their compound nature is indicated by the beautiful pattern, which is too regular in the imitations now common. Even the shavings and leavings can be welded and moulded into large pieces. The stripping of the shields has been described by Sir E. Tennent. "If taken from the animal after death and decomposition, the colour of the shell becomes clouded and milky, and hence the cruel expedient is resorted to of seizing the turtles as they repair to the shore to deposit their eggs, and suspending them over fires till heat makes the plates on the dorsal shields start from the bone of the carapace, after which the creature is permitted to escape to the water. At Celebes, where the finest tortoise-shell is exported to China, the natives kill the turtles by blows on the head, and immerse the shell in boiling water to detach the shields. Dry heat is only resorted to by the unskilful, who frequently destroy the tortoise-shell in the operation." The cruel process described above is resorted to "for economy's sake," the Singhalese believing that such maltreated turtles regenerate the shields, to be caught and shipped again. Since none of them are actually re-caught in the mutilated condition, this is looked upon as a proof of the correctness of the treatment. It is more likely that they die.

New shields can be reproduced only if the underlying Malpighian layer of cells (_cf._ Fig. 68, B, p. 323) is not killed by the roasting. However, Dr. Charles Hose, with his long experience in Borneo, is positive that numerous individuals are there caught which have imperfectly mended shells, the shields of which do not imbricate, are thin, and almost worthless.

It is commonly believed that the same individuals return again and again to the same spot for laying. This is very likely the case. Tennent mentions that in the year 1826 a Hawksbill was taken near Hambangtotte, which bore a ring attached to one of its fins, that had been placed there by a Dutch {387}officer thirty years before, with a view of establishing the fact of these recurring visits to the same beach. The same homing instinct has been observed in some females of the Green Turtle, which, having been brought from the Tortugas Keys to Key West off the south end of Florida, escaped, and were, a few days later, re-caught at the Tortugas. On the other hand, experiments made with turtles at Ascension are said to have had no result.

_Thalassochelys_, with five pairs of costal shields. The carapace is completely ossified in the adult, leaving no fontanelles between the ribs and the marginals.

_Th. caretta_ (the "Loggerhead Turtle").–The shields of the carapace imbricate only in young specimens, in the adult they become smooth and juxtaposed. The margin is serrated posteriorly. The carapace of the young has three strong keels. The intergular shield is very small or absent. The marginals, including the nuchal, usually number 23, rarely 25. The large head is armed with hooked jaws, the crushing surface of the horny upper beak has a median prominent ridge. The top of the head has a pair of shields in front of the unpaired frontal. The flippers of the young have claws on the first and second digits; in the adult usually only that of the first digit remains. The general colour of the shell is uniform brown above, yellowish below. Very young specimens are uniform dark brown or blackish above and below.

Large individuals have a shell about three feet and a half in length. The Loggerhead is carnivorous, and is commercially of no value. Its habits seem to be the same as those of the other Turtles, but it has a much wider distribution. Besides all the tropical and intertropical seas, it inhabits the Mediterranean, and is an accidental visitor to the western coasts of Europe, especially Portugal and the Bay of Biscay. It has been caught several times on the coast of Belgium, and an old female containing 1150 eggs was captured in 1894 on the Dutch coast. In 1861 one was caught near Penman, on the coast of Banffshire, and a second in the completely land-locked Loch Lomond.[137] It has been more frequently recorded from the coast of Devon and Cornwall.

The most interesting feature of the Loggerhead is the {388}astonishing variability in the number of the horny shields of the carapace. The normal number of shields of the carapace, leaving out the marginals and counting the nuchal as the first neural, is 6 neurals and 5 pairs of costals, in all 16. The greatest number of dorsal shields observed is 8 neurals and 8 pairs of costals, in all 24. Many of the intermediate combinations have been observed, there being, for instance, specimens with 8 neurals and 16, 14, 13, 12, or 11 costals, the latter not being always in pairs, but unequal on the right and left sides; or there are 7 neurals with 20 to 16 costals, or 6 neurals with 20, 19, 18, 17, or 16 costals. The interesting fact in connexion with these variations is, moreover, that some of the shields are much smaller than the others, sometimes mere vestiges in all stages of gradual suppression, and that the abnormalities are much more common in babies and small specimens than in adults. The importance of these "orthogenetic" variations has been discussed on p. 326.

SUB-ORDER 2. PLEURODIRA.–_Neck bending laterally and tucked away in the niche formed between the anterior portion of the carapace and plastron. Pelvis ankylosed to the shell, the broadened tops of the ilia to the carapace, the distal ends of the pubes and ischia to the plastron._

Freshwater tortoises, almost entirely carnivorous, inhabiting South America, Australia, Africa, and Madagascar. Fossil forms are known from the Jurassic epoch onwards.

Owing to the strong connexion of the iliac bones with the costal plates the sacrum has become practically abolished, the sacral ribs being reduced to one pair (the posterior of the original two pairs) or being absent. The centra of the cervical vertebrae articulate by cup and ball joints. The formation of the temporal region of the skull varies considerably in the three families, some genera lacking the complete zygomatic arch, while others have a narrow parieto-squamosal arch bridging over the temporal fossa, or the latter is completely roofed over by the laterally expanded parietal, which meets the jugal and quadrato-jugal. The quadrate is always trumpet-shaped; the rim of the tympanum is complete, but the posterior part of the trumpet remains open. The basisphenoid, pterygoids, and palatines form a broad and flat roof to the mouth. The vomer is large, and separates the palatines in the Chelydidae; it is very much {389}reduced or absent in the Pelomedusidae, in which the palatines meet. All the Chelydidae, except _Chelys_, have nasal bones which remain distinct from the prefrontals. The choanae lie in front of the palatines, divided by the vomer when this is present, but they are not roofed in ventrally.

The ilia are solidly ankylosed in the adult with the neighbouring costal plates, mostly with the last two pairs, sometimes also with the pygal plate. The lateral processes of the pubes fuse with the xiphiplastra. The ischia are also attached to the same plastral elements.

The carapace is flat and completely ossified. The nuchal plate is always conspicuous, much larger than the neurals, and these are often reduced by being encroached upon by the eight pairs of costal plates, which then meet in the dorsal line. In _Sternothaerus_ all the eight neurals are present and form a continuous row. In most of the other genera they are reduced to seven, the last being squeezed out. In _Rhinemys_ they are reduced to the second, third and fourth and an isolated fifth, and in _Hydraspis_ they are all gone. The pygal plate is always, even in _Sternothaerus_, separated from the last neural by the eighth pair of costals. The marginals number 23, but in _Carettochelys_ only 21.

The carapace is covered with horny shields, except in _Carettochelys_. The nuchal is absent in the Pelomedusidae and in a few Chelydidae (_Elseya_ and a few species of _Emydura_). In _Hydromedusa_ the nuchal is shut in by the anterior marginals, simulating a sixth neural. The plastron is composed of the usual nine elements, but the Pelomedusidae possess an additional pair, the meso-plastra, inserted between the hyo- and hypo-plastra. The bridge is strong, connected with the carapace by suture. In _Sternothaerus_ the front lobe of the plastron is movable. The intergular shield is always present; it is terminal, forming part of the front margin, except in _Chelodina_, where this shield, although large, is shut in behind the gulars (cf. Fig. 61, 4 and 5, p. 315).

Although the Pleurodira are a peculiarly specialised group, one of the oldest Chelonian fossils known seems to belong to them. _Proganochelys_, represented by a complete shell, nearly 2 feet long, has been found in the Upper Keuper Sandstone of Würtemberg. _Plesiochelys_, of the Upper Jurassic of Switzerland, has eight neural and three supracaudal plates, but is without the {390}ischiadic plastral ankylosis. _Pleurosternum_, of the English and Continental Purbeck beds, has meso-plastral plates like the recent Pelomedusidae. _Rhinochelys_, of the Cambridge Greensand, has a broad parieto-postfrontal roof, and large nasal bones. Forms like _Podocnemis_, now restricted to South America, occur in the Eocene of Europe. One of the most aberrant Chelonians is _Miolania_, from the Plistocene of Queensland and from Lord Howe's Island, remarkable for its huge size and the thick armour on the head and tail; the head especially carries large paired projections, one pair of which extends horizontally like powerful horns, recalling the queer Theromorphous _Elginia_.

We divide the recent Pleurodira into three families, of which that of _Carettochelys_ stands apart by its paddle-shaped limbs and the absence of horny shields. The Pelomedusidae and Chelydidae are closely allied. The former are not Australian, and are externally distinguished by the absence of a nuchal shield.

FAM. 1. PELOMEDUSIDAE.–Neck completely retractile within the shell. Carapace without a nuchal shield. The plastron is composed of eleven plates, there being besides the unpaired endo-plastron a pair of meso-plastra, situated between the hyo- and hypo-plastra; but these meso-plastra meet in the middle line in _Sternothaerus_ only, while in _Podocnemis_ and _Pelomedusa_ they are restricted to small pieces on the bridge, widely separated from each other by the usual hyo- and hypo-plastral suture. A nuchal shield is absent; there are twenty-four marginal and thirteen plastral shields, inclusive of the conspicuous intergular. The temporal fossa is widely open, except in _Podocnemis_, where it is partly roofed in by the meeting of the much-expanded quadrato-jugal with the parietal. The palatine bones are in median contact, not separated by the vomer. Nasal bones being absent, the large prefrontals meet in the middle line. The second cervical vertebra is biconvex.

This family is now represented by only three genera, with about fifteen species in Africa, Madagascar, and South America.

_Sternothaerus._–Skull without a bony supratemporal roof. Meso-plastra large, extending right across the plastron. Anterior lobe of the plastron movable, the hinge passing between the hyo- and meso-plastral plates, and between the pectoral and abdominal shields. Fore- and hind-limbs with five short digits and claws. Several species in tropical and southern Africa, and {391}in Madagascar. _S. derbianus_ in West Africa, from the Gambia to Angola, is the largest species, with a shell nearly one foot in length.

_Pelomedusa._–Skull with a slender parieto-squamosal arch. Meso-plastra small and lateral. Plastron without a hinge. Fore- and hind-limbs with five very short digits and five claws. Top of the head with one pair of shields between the eyes, and with a large interparietal and a pair of parietals behind.

_P. galeata_, the only species, occurs in Madagascar and nearly the whole of Africa south of the Sahara, from the Cape to Abyssinia, and in the Sinaitic peninsula. The shell, less than one foot in length, is much depressed and is obtusely keeled; brown above with black spots; brownish-yellow below. The short and broad head is coloured like the rest, without ornamentation. In Somaliland this species sleeps hidden on land during the dry seasons, from July to the end of September, and from January to March, and appears at once after the rains have set in.

_Podocnemis._–With a supratemporal roof formed by the junction of the parietal with the quadrato-jugal. Meso-plastra small and lateral. Fore- and hind-limbs broadly webbed, with five and four claws respectively. The fore-arms and the outer edges of the hind-feet with several conspicuous shields, hence the generic name. Head with an interparietal, two parietals, and a narrow unpaired shield between the eyes. The tail is very short. The carapace is flat and broad, strongly serrated on the posterior margin. Chin with one or two short barbels. Several species in South America, chiefly in the basin of the Amazon, and one in Madagascar.

_P. expansa._–Very common in Tropical South America, east of the Andes. The female, which is much larger than the male, has a shell nearly three feet in length. Olive-brown above with darker patches; yellowish below. With a few yellow spots above and behind the eyes, and on the parietal region. The "Arrau" turtle is of great commercial importance on account of the eggs, which are periodically collected in enormous quantities, chiefly for the oil. This is either eaten, like the eggs themselves, or used for burning in lamps, or as an addition to tar. The turtles are likewise eaten by man and beast. Thousands of the little creatures are snapped up by Jabiru storks, alligators, and fishes; the adults fall an easy prey {392}to the prowling jaguar, which turns them over on to their backs and neatly cleans out the flesh with its sharp and powerful claws.

Fertilisation takes place in the water, the eggs are deposited on land, in sand-banks, the female digging a hole about two feet deep and covering up the numerous soft-shelled eggs with sand. The time of deposition is the early hours of the morning, but the season depends upon the beginning of the principal rains, since the young are hatched shortly before the torrential rains. This season differs considerably in the various countries. The hatching takes about forty days; the eggs are consequently laid in the Amazon countries during the months of September to November, in the Orinoco district in March. This species lives in the pools of the inundated forests, and when these are dried up, the animals retire into the rivers themselves. Their food consists mainly of the fruit dropping down from the trees.

Bates, in his delightful book, _The Naturalist on the River Amazon_, gives the following lively and exhaustive account of his experience with these turtles:–

"I accompanied Cardozo in many wanderings on the Solimoes, during which we visited the 'praias' (sand islands), the turtle pools in the forests, and the by-streams and lakes of the great desert river. His object was mainly to superintend the business of digging up turtle eggs on the sandbanks, having been elected commandant for the year by the municipal council of Ega, of the 'praia real' of Shimuni, the one lying nearest to Ega. There are four of these royal praias within the Ega district, a distance of 150 miles from the town, all of which are visited annually by the Ega people for the purpose of collecting eggs and extracting oil from their yolks. Each has its commander, whose business is to make arrangements for securing to every inhabitant an equal chance in the egg harvest, by placing sentinels to protect the turtles whilst laying, and so forth. The pregnant turtles descend from the interior pools to the main river in July and August, before the outlets dry up, and there seek in countless swarms their favourite sand-islands; for it is only a few praias that are selected by them out of the great number existing. The young animals remain in the pools throughout the dry season. These breeding places of turtles then lie 20 to 30 or more feet above the level of the river, {393}and are accessible only by cutting roads through the dense forest....

"We found the two sentinels lodged in a corner of the praia, where it commences at the foot of the towering forest-wall of the island, having built for themselves a little rancho with poles and palm-leaves. Great precautions are obliged to be taken to avoid disturbing the sensitive turtles, who, previous to crawling ashore to lay, assemble in great shoals off the sand-bank. The men, during this time, take care not to show themselves, and warn off any fisherman who wishes to pass near the place....

"I rose from my hammock by daylight, shivering with cold; a praia, on account of the great radiation of heat in the night from the sand, being towards the dawn the coldest place that can be found in this climate. Cardozo and the men were already up watching the turtles. The sentinels had erected for this purpose a stage about fifty feet high, on a tall tree near their station, the ascent to which was by a roughly made ladder of woody lianas. They are enabled, by observing the turtles from their watch-tower, to ascertain the date of successive deposits of eggs, and thus guide the commandant in fixing the time for the general invitation to the Ega people.

"The turtles lay their eggs by night, leaving the water, when nothing disturbs them, in vast crowds, and crawling to the central and highest part of the praia. These places are, of course, the last to go under water when, in unusually wet seasons, the river rises before the eggs are hatched by the heat of the sand.... The hours between midnight and dawn are the busiest. The turtles excavate with their broad webbed paws deep holes in the fine sand; the first-comer, in each case, making a pit about three feet deep, laying its eggs (about 120 in number), and covering them with sand; the next making its deposit at the top of that of its predecessor, and so on until every pit is full. The whole body of turtles frequenting a praia does not finish laying in less than fourteen or fifteen days, even when there is no interruption. When all have done, the area (called by the Brazilians 'taboleiro') over which they have excavated is distinguishable from the rest of the praia only by signs of the sand having been a little disturbed.

"I mounted the sentinel's stage just in time to see the turtles retreating to the water on the opposite side of the sand-bank, {394}after having laid their eggs. The sight was well worth the trouble of ascending the shaky ladder. They were about a mile off, but the surface of the sands was blackened with the multitudes which were waddling towards the river; the margin of the praia was rather steep, and they all seemed to tumble head first down the declivity into the water.... Placards were posted up on the church doors at Ega, announcing that the excavation on Shimuni would commence on the 17th of October, and on Catuá, sixty miles below Shimuni, on the 25th. By the morning of the 17th some 400 persons were assembled on the borders of the sand-bank, each family having erected a rude temporary shed of poles and palm-leaves to protect themselves from the sun and rain. Large copper kettles to prepare the oil, and hundreds of red earthenware jars, were scattered about on the sand.

"The excavation of the taboleiro, collecting the eggs, and purifying the oil, occupied four days. All was done on a system established by the old Portuguese governors, probably more than a century ago. The commandant first took down the names of all the masters of households, with the number of persons each intended to employ in digging; he then exacted a payment of 140 reis (about 4d.) a head towards defraying the expense of sentinels. The whole were then allowed to go to the taboleiro. They ranged themselves round the circle, each person armed with a paddle, to be used as a spade, and then all began simultaneously to dig on a signal being given–the roll of drums–by order of the commandant. It was an animating sight to behold the wide circle of rival diggers throwing up clouds of sand in their energetic labours, and working gradually towards the centre of the ring. A little rest was taken during the great heat of mid-day, and in the evening the eggs were carried to the huts in baskets. By the end of the second day the taboleiro was exhausted; large mounds of eggs, some of them four to five feet in height, were then seen by the side of each hut, the produce of the labour of the family.

"In the hurry of digging, some of the deeper nests are passed over; to find these out, the people go about provided with a long steel or wooden probe, the presence of the eggs being discoverable by the ease with which the spit enters the sand. When no more eggs are to be found, the mashing process begins. {395}The egg, it may be here mentioned, has a flexible or leathery shell; it is quite round, and somewhat larger than a hen's egg. The whole heap is thrown into an empty canoe and mashed with wooden prongs; but sometimes naked Indians and children jump into the mass and tread it down, besmearing themselves with yolk, and making about as filthy a scene as can well be imagined. This being finished, water is poured into the canoe, and the fatty mass is then left for a few hours to be heated by the sun, on which the oil separates and rises to the surface. The floating oil is afterwards skimmed off with long spoons, made by tying large mussel-shells to the end of rods, and purified over the fire in copper kettles.

"The destruction of turtle eggs every year by these proceedings is enormous. At least 6000 jars, holding each three gallons of the oil, are exported annually from the Upper Amazons and the Madeira to Para, where it is used for lighting, frying fish, and other purposes. It may be fairly estimated that 2000 more jarfuls are consumed by the inhabitants of the villages on the river. Now, it takes twelve basketfuls of eggs, or about 6000, by the wasteful process followed, to make one jar of oil. The total number of eggs annually destroyed amounts, therefore, to 48 millions. As each turtle lays about 120, it follows that the yearly offspring of 400,000 turtles is thus annihilated. A vast number, nevertheless, remain undetected; and these would probably be sufficient to keep the turtle population of these rivers up to the mark, if the people did not follow the wasteful practice of lying in wait for the newly-hatched young, and collecting them by thousands for eating; their tender flesh, and the remains of yolk in their entrails, being considered a great delicacy. The chief natural enemies of the turtle are vultures and alligators, which devour the newly-hatched young as they descend in shoals to the water. These must have destroyed an immensely greater number before the European settlers began to appropriate the eggs than they do now. It is almost doubtful if this natural persecution did not act as effectively in checking the increase of the turtle as the artificial destruction now does. If we are to believe the tradition of the Indians, however, it had not this result; for they say that formerly the waters teemed as thickly with turtles as the air does now with mosquitoes. The universal {396}opinion of the settlers on the Upper Amazon is, that the turtle has very greatly decreased in numbers, and is still annually decreasing.

"The principal object of another expedition was to search certain pools in the forest for young turtle. We started from the praia at sunrise on the 7th of October in two canoes, containing twenty-three persons, nineteen of whom were Indians. The pool covered an area of about four or five acres, and was closely hemmed in by the forest, which, in picturesque variety and grouping of trees and foliage, exceeded almost everything I had yet witnessed. The margins for some distance were swampy, and covered with large tufts of fine grass. The pool was nowhere more than five feet deep, one foot of which was not water, but extremely fine and soft mud.

"Cardozo and I spent an hour paddling about. The Indians seemed to think that netting the animals, as Cardozo proposed doing, was not lawful sport, and wished first to have an hour or two's old-fashioned practice with their weapons. I was astonished at the skill which they displayed in shooting turtles from little stages made of poles and cross pieces of wood. They did not wait for their coming to the surface to breathe, but watched for the slight movements in the water which revealed their presence underneath. These little tracts on the water are called the siriré; the instant one was perceived an arrow flew from the bow of the nearest man, and never failed to pierce the shell of the submerged animal. When the turtle was very distant, of course the aim had to be taken at a considerable elevation, but the marksmen preferred a longish range, because the arrow then fell more perpendicularly on the shell, and entered it more deeply.

"The arrow used in turtle-shooting has a strong lancet-shaped steel point fitted into a peg, which enters the tip of the shaft. The peg is secured to the shaft by twine, being some thirty or forty yards in length, and neatly wound round the body of the arrow. When the missile enters the shell the peg drops out, and the pierced animal descends with it towards the bottom, leaving the shaft floating on the surface. This being done the sportsman paddles in his canoe to the place, and gently draws the animal by the twine, humouring it by giving it the rein when it plunges, until it is brought again near the surface, when {397}he strikes it with a second arrow. With the increased hold given by the two cords he has then no difficulty in landing his game.

"By mid-day the men had shot about a score of nearly full-grown turtles. Cardozo then gave orders to spread the net.... Three boat loads, or about eighty, were secured in about twenty minutes. They were then taken ashore and each one secured by the men tying the legs with thongs of bast.

"When the canoes had been twice filled we desisted after a very hard day's work. Nearly all the animals were young ones, chiefly, according to the statement of Pedro, from three to ten years of age; they varied from 6 to 18 inches in length, and were very fat. Cardozo and I lived almost exclusively on them for several months afterwards. Roasted in the shell they form a most appetising dish. These younger turtles never migrate with their elders on the sinking of the waters, but remain in the tepid pools, fattening on fallen fruits, and, according to the natives, on the fine nutritious mud. We captured a few full-grown mother turtles, which were known at once by the horny skin of their breast plates being worn, telling of their having crawled on the sand to lay eggs the previous year. They had evidently made a mistake in not leaving the pool at the proper time, for they were full of eggs, which, we were told, they would, before the season was over, scatter in despair over the swamp. We also found several male turtles, or capitaris, as they are called by the natives. These are immensely less numerous than the females, and are distinguishable by their much smaller size, more circular shape, and the greater length and thickness of their tails. Their flesh is considered unwholesome, especially to sick people having external signs of inflammation."

The most recent account of these water tortoises is that published by Dr. Goeldi from the MS. of João Martins da Silva Continho, a former resident at Manáos on the Middle Amazon. The "Tartaruga" (the Portuguese name for turtles) live from January to July in the inundated, quiet backwaters of the forest-region, feeding upon the various seeds of palms as these ripen and drop successively; rarely, and only when hard up, they are carnivorous. The creatures hide under water below the trees, when they are espied by the Indians, who dive down to a depth of twenty and more feet to catch them in their arms. The {398}civilised Indians use a steel-pointed lance of hard wood, about 10 feet in length. A string connects the point with the shaft around which it is wound. When stuck into the tortoise the shaft and point part; the string is either tied to the boat or to a little float of light wood. In other districts an arrow with a string is employed.

In August, when the water subsides, the tortoises return to the rivers, and the entrance of the lagoon is closed with nets. A number of boats with long poles drive them with much noise towards the entrance. On their way to the rivers the tortoises always go up-stream, and this is called the "arribaçaõ das tartarugas," the ascent of the turtles. The fishermen post themselves at shallow spots or on sand-banks, and wait for the creatures which come up to find a place for landing and laying. The arrows employed are called _sararaca_, _i.e._ a thing which can be disjointed; they are about 4 feet long, and consist of a _gomo_ or internodium of wood 9 inches long with a one- or two-barbed steel point, and the shaft into which the _gomo_ fits loosely. The _gomo_ is, moreover, connected with the shaft by a string made of palm-fibres about 30 feet in length, partly wound round the shaft, which ultimately acts as a float.

The laying takes place from the end of September into October. Some of the parents seem to reconnoitre on land for a few days. As a rule only females do this, and the natives say that they are led by a "_mestra_." The laying takes place early in the morning. The number of females is so great that they often block the way of the boats, and make a great noise by knocking against their neighbours' shells. Each digs a hole about 18 inches or 2 feet deep, and lays from 80 to 200 eggs. Sometimes the laying individual is entirely buried by its neighbours which are scraping their own holes.

In some districts the eggs are wanted for "manteiga" (Portuguese for butter); and the turning over, or _viraçaõ_ of the tortoises takes place later. In other districts they are caught before the eggs are laid, and this barbaric and destructive custom was formerly forbidden by the people themselves. Although the provincial assembly tried to reinstitute the old reasonable customs, the inspectors are often got over by bribery.

There are two ways of extracting the oil from the eggs. To get the thick oil used, mixed with tar, for shipbuilding, caulking, {399}etc., the eggs are heaped up for five days and then worked. The fluid oil for lighting is made from fresh eggs, which are put into a boat and then trampled out with the feet. The oil is drawn off into large earthen jars and put on the fire. Then it is rapidly cooled. The best oil, used for frying fish, is that which is gained from the roasted tortoises themselves. Fresh eggs are either fried or taken with sugar, or mixed with manioca-flour and water. The young, which are hatched in January, are likewise eaten fried, or they are preserved in the fat of the parents.

An average tortoise yields 5 lbs. of fat, costing on the spot two milreis. The whole full-grown animal, of one yard in length, costs the same, and its meat is sufficient to sustain a family of six people for three days. To make 24 lbs. of oil requires 3000 eggs. Two or three tortoises would yield the same amount from their fat. Consequently the destruction of the eggs causes an enormous waste, and is after all the least economical procedure. In the year 1719, 192,000 lbs. were exported from the Alto Amazonas, representing 24,000,000 eggs. In 1700 there were still plenty of tortoises 50 leagues above the mouth of the Para river. Now there is no assembly of more than fifteen tortoises to be found anywhere within 300 leagues from Para to the mouth of the Rio Negro. On the Rio Madeira, from the mouth to the first cataract, 186 leagues distance, there are now only two regular nesting localities. The upper Solimoes and the Rio Yapura are still rich. Near Ega are regular tortoise-ponds, called "curral," which yield sufficient support to their owners; the animals are fed with manioca-flour and leguminous plants.

FAM. 2. CHELYDIDAE.–The neck bends under the margin of the carapace, but remains partly exposed. The nuchal shield is absent except in two Northern Australian species. There are twelve pairs of marginal shields. The plastron is composed of nine plates, and is covered with thirteen shields, one of which is the conspicuous intergular. The temporal region of the skull shows great diversity. It is quite open in _Chelodina_, covered in by broad expansions of the parietal bones in _Platemys_, _Emydura_, and _Elseya_, or bridged over by a parieto-squamosal arch, which is very slender in _Rhinemys_, strong in _Chelys_ and _Hydraspis_. The palatine bones are separated by the vomer; the nasals are variable, mostly present, but the prefrontals are always small, and separated {400}by the frontals. The fifth and eighth cervical vertebrae are biconvex.

This family, still represented by nearly thirty species, which are divided into eight genera, is restricted to Notogaea, namely, South America and Australia.

_Chelys fimbriata_, the "Matamata," the only species of this genus, inhabits the rivers of Guiana and Northern Brazil. Besides the nuchal, there are seven neural plates; the last pair of costals form a median suture. Nasal bones are absent. The jaws are very weak. The Matamata has a very peculiar appearance. The nose is produced into a long, soft tube, at the end of which open the tiny nostrils. The eyes are very small, and the orbits are placed very near the anterior end of the skull, while the parietal {401}region is broad and much elongated (Fig. 87, p. 400). The quadrates are drawn out into trumpet-shaped tubes. The hyoid apparatus is very large, with enormous anterior and posterior horns. The head and neck are as long as or even longer than the carapace, which is covered with thick, lumpy shields. The skin of the thick neck, of the sides and under parts of the head, is produced into many soft arborescent excrescences or fimbriae, those of the chin and throat and the large ear-flaps being movable at will, and probably used to attract fishes and other prey. The tail is very short. The fore- and hind-limbs are webbed, the former with five, the latter with four claws. Old specimens, which reach a total length of three feet, are uniformly dark brown, and look like a log covered with rough bark. The young are far less ugly, with black and yellow spots on the shell, and with dark stripes along the neck.

Very little is known about the habits of this peculiar creature. It is said to lie submerged in the water, waiting for fishes, frogs, or tadpoles, which are attracted by the playing motions of its cutaneous excrescences. The jaws being so weak, and being covered with a partly soft lip-like skin, it is probable that they are not used for seizing the prey, but that the latter is engulfed into the mouth with the inrush of water into the throat. {402}That this can be widened enormously is indicated by the greatly developed hyoid apparatus.

_Chelodina._–The neck is long and slender, the head small and smooth. The nuchal is terminal; the intergular is large. The neural plates are completely suppressed, all the eight pairs of costal plates meeting in the middle line. The shell is very flat. Anterior and posterior limbs entirely webbed, and with only four claws. The tail is very short. Three species in Australia, one in New Guinea.

_Ch. longicollis_ reaches a shell-length of ten inches. It inhabits Southern Australia. The illustrations make a detailed description unnecessary. The colour of the dorsal shield is uniformly dark rich brown, while the shields of the under surface are yellow, with broad dark brown lines along the sutures. These "long-necked Chelodines" have a striking appearance, when they swim or creep about, with the neck either stretched out straight or bent horizontally in an S-shape. The whole creature looks neat and elegant; the iris is pale yellow, and gives the eye a very intelligent expression. They keep well in captivity, provided they are given the choice of land and water. My own prefer to spend most of the day on land, preferably under the ledge of a stone, or perched upon the stone itself if the latter is in the shade, and not too much exposed to view. There they lie motionless, with the neck neatly tucked under the shell, either to the right or to the left. Although the eyelids may be closed, they can see well enough, owing to the transparent condition of the lower lid. They feed in the water upon soft animals, as for instance worms, smooth caterpillars, cockroaches or little frogs; and they also take meat readily, provided this is moved about. The food is invariably taken with a quick sideward jerk of the neck and head.

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My specimens soon became so tame that they left the water, and ran up to me with the necks stretched to their full length, then snatching the bit of food, and retiring into the pond to swallow it. When left to themselves they are rather nocturnal in their feeding habits. Now and then they tuck themselves away for weeks without feeding, for instance when they go through a regular term of {404}aestivation in the summer. The last winter they spent buried in the moss, but occasionally, especially on bright and sunny days, they went into the water for a few hours, chiefly to drink, but sometimes also to take a little food.

_Hydromedusa_, a South American genus, has a neck even longer than that of _Chelodina_, which it much resembles externally. But the nuchal shield, large and broad transversely, is situated behind the anterior marginals, looking therefore like a sixth neural shield. The neural plates form a continuous row, only the last pair of costal plates meeting in the middle line. _H. tectifera_ occurs in Southern Brazil, and in the La Plata. The shell is dark brown above; yellowish, with dark spots, below; the head and neck are olive-coloured, adorned with a broad white, black-edged band on either side. Fore- and hind-limbs broadly webbed, and with four claws. Total length of the shell about eight inches.

FAM. 3. CARETTOCHELYDIDAE.–The shell is covered with soft skin instead of horny shields. The limbs are transformed into paddles, with elongated digits, and have only two claws. The neck is short, and not retractile. In other respects the skeleton, notably the plastron, pelvis, and skull, conform with the Pleurodirous type. Only one species, _Carettochelys insculpta_, still imperfectly known, from the Fly River, New Guinea. Length of the shell of the only complete specimen about 18 inches. This peculiar creature seems to stand in the same relation to the typical Pleurodira, as do the Chelonidae to the Testudinidae, except for the complete reduction of the horny shields upon the shell, recalling in this respect _Sphargis_ and _Trionyx_.

SUB-ORDER 3. TRIONYCHOIDEA.–The shell is very flat, oval, or almost round, and is covered with soft, leathery skin instead of with horny shields. The limbs are broadly webbed, and only the three inner digits are provided with claws. Carnivorous, found in the rivers of Asia, Africa, and North America.

The head and neck are completely retractile, bending by a sigmoid curve in a vertical plane like that of the Cryptodira. The jaws are concealed by soft, lip-like flaps, and the nose forms a soft short proboscis. The ear is hidden. The skull, Fig. 91, is flat, with three long posterior processes, formed by the supra-occipital above, and the squamosals on either side. The whole temporal region forms a wide, shallow fossa, without any {405}indication of being arched or bridged over. The premaxilla is extremely small, unpaired, not even reaching the nasal cavity or the vomer. The maxillaries are correspondingly enlarged, surrounding the choanae, which are separated by the narrow vomer. The palatines form a median suture, and are joined behind by the long basisphenoid, which separates the long pterygoids from each other. The quadrate is trumpet-shaped, with a posterior notch for the stapes. The zygomatic arch is complete, and is formed by the quadrato-jugal and the jugal; the latter joins the maxillary and postfrontal, mostly reaching the orbit; in some cases it also just meets the parietal, thereby adding to the strength of the postorbital arch. The prefrontals are large; nasals are absent. The mandible is remarkable for the great development of the coronoid process.

The pubic and ischiadic bones enclose a large heart-shaped foramen, and are free from the plastron; the ilia are attached only to the sacral ribs. The carapace is peculiar in so far as it is very incomplete peripherally, the ribs extending considerably beyond the costal plates, nor are they joined by marginal plates, which are absent, unless they are represented by a few small ossifications imbedded in the posterior marginal flap of the disc (_Emyda_ of India). The rim of the disc is always formed by a horizontal, cutaneous, very flexible flap. All the dorsal plates have a rough upper surface, vermiculated or rugose, as usual with such dermal bones, which have lost most of or all their horny covering, and have sunk more deeply into the skin. The {406}nuchal plate has usually a pair of rib-like processes. The neurals form a continuous series, except in the African _Cyclanorbis_, in which they are much reduced in size, and separated by the costal plates.

The plastron is imperfect, all its constituent nine elements being only loosely connected with each other, and there remains a wide median vacuity between the lateral elements. Most of these plastral bones are reduced to splints, which, instead of meeting by regular sutures, loosely interdigitate with their jagged edges. In the young all these ventral elements are deeply imbedded in the soft, leathery skin, and they do not at all resemble in appearance those of the dorsal side. With age they develop upon their ventral surface stronger and denser ossifications, which ultimately broaden out, sometimes beyond the original underlying bone, and assume the characteristic vermiculated surface-appearance. This is undoubtedly a process of exostosis, a step towards revival of that armour which had been much reduced ancestrally. To appreciate this condition, it is at least suggestive that these mud-tortoises, when kept in the usual hard-bottomed tanks, invariably become sore, the skin wearing through where the imbedded plastral bones touch the ground. Thus what is crammed into the short life of a captive individual, is in the natural course of events spread over many generations, whereby it has ceased to be pathological, and has become a comparatively new, tertiary, but regular feature.

It is not open to much doubt that the characteristic features of the Trionychoidea are not primitive but secondary. This is indicated by the whole structure and behaviour of the carapace and plastron. The softening of the whole shell, the loss of the horny shields, the reduction of the claws, are the direct and almost unavoidable results of life in muddy waters.

Geologically they do not seem to be very old. They appear, already referable to the genus _Trionyx_, in the Upper Cretaceous strata of North America. In the Lower and Middle Tertiary strata many species existed in North America and in Europe, and it is of great importance that in these species the costal plates were much broader, and the marginal plates better developed, than in the recent forms. Now their half-dozen genera, with about twenty-four species, are confined to North America, the tropical and warmer parts of Asia, and the Malay {407}Islands, and to Africa from the Nile to the Senegal and to the Congo.

The habits of Trionychoidea have found few observers. According to L. Agassiz,[138] they live in the muddy bottom of shallow waters, burying themselves in the soft mud, with only the head, or a small part of it, exposed. They breathe without moving the body, by raising up the long neck and carrying the leathery snout above water. When moving through the water they strike horizontally with both pairs of limbs, alternating, however, the right and left; but when they start suddenly, the front limbs are seen moving together towards the tip of the snout, and then striking simultaneously backward with great power. As the shield does not project forward, the fore-limbs usually move beyond the shield, and as its outer edge is sharp, and the feet are broad, their webs reach above as well as below the plane of that edge, so that the water is driven partly over and partly under it. When they move along the bottom, the limbs still move horizontally, the webs striking against the water, and the inner toes, those with the claws, against the bottom. They also bury themselves horizontally, becoming covered by only a thin layer of mud. They readily resort to the shell for protection. The neck and head are withdrawn entirely, the loose skin rolling off from the greater part of the neck; and the skin of the legs also slips off, as far as the elbows and knees. In confinement they exhibit great quickness; their movements are abrupt and unsteady, except when they swim rapidly in one direction. They then dart their long and slender neck quickly forwards or sideways and upwards, as snakes do, and bite in the same way, striking suddenly. Their temper is bad or even ferocious, and large specimens are quite dangerous.

Their food consists of all sorts of aquatic animals, fish, frogs, and molluscs, for instance _Anodonta_ and _Paludina_. According to the different diet, many species develop a peculiar kind of dimorphism, a reasonable explanation of which has been given by Boulenger. In the young the horny coverings of the jaws are sharp, with cutting edges, and in those specimens which keep to a diet of fish and other soft creatures, the jaws remain in the same condition. But in those which take to living upon molluscs, the hard shells of which they have to crush, the horny edges are {408}worn down; and broad, thick, horny, crushing pads are developed in their stead, the supporting parts of the jaws becoming more massive. The masticatory muscles are likewise enlarged, and a tubercle grows upon the lower border of the jugal bone, whence arises part of the masseter muscle.

The eggs are round, thick-shelled, but very brittle; they are laid in the sand above the level of the water, and this is the chief occasion on which these tortoises creep on land.

_Trionyx._–The plastron has no special cutaneous valves for the concealment of the hind-limbs. This is the principal genus, with the greatest number of species and the widest distribution, the latter coinciding with that of the whole family. The upper surface of the shell of young specimens frequently forms numerous longitudinal ridges or series of little horny tubercles which disappear with age.

_T. ferox_, the commonest "Soft-shelled Turtle" of the United States. Olive above with scattered, small, round, black spots; young with conical, spine-like tubercles, especially on the nuchal border and on the posterior portion of the shell, which has a pale, black-edged border. A light, black-edged streak passes through the eye and joins its fellow on the snout. The limbs are olive brown, spotted and marbled with black. The under parts of the shell are white. Very large specimens have a shell 18 inches in length and 16 inches wide. Holbrook gives the following account of its habits:–

"A voracious, carnivorous creature. They reside most constantly in the water, swim with rapidity, and choose for their retreat holes under the banks of rivers, or under rocks; and not unfrequently the trunk of some huge forest tree, fallen into the stream, affords them shelter. Sometimes they leave the water and conceal themselves in the mud: I have frequently seen them thus buried to the depth of 2 or 3 inches, leaving only a small breathing hole for the long neck and narrow head, which is occasionally thrust out, but most commonly it is retracted so that one would pass near without observing their habitation; and if seen, it might easily be mistaken for the residence of some large insect. At other times they may be seen in numbers on rocks in shallow water, basking in the sun, apparently asleep. They bite severely when provoked, darting forward with great velocity the long neck and head, and not unfrequently spring upward at the same time and make a loud hiss.

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In the month of May the females seek sandy places along the banks of the waters they inhabit to lay their eggs, generally about sixty in number; and it is remarkable that, though their motions are slow and difficult on dry land, yet at this season they sometimes mount hillocks several feet high. The flesh affords the most delicate food, surpassing that even of the Green Turtle. The geographical distribution is interesting. It inhabits the Savannah as well as all those rivers that empty into the northern borders of the Gulf of Mexico; it ascends up the broad Mississippi, and is found in all its tributaries, even to the very foot of the Rocky Mountains; it abounds in the chain of great northern lakes both above and below the Falls of Niagara, and is common in the Mohawk, a tributary of the {410}Hudson river; but it is not found in any other Atlantic stream between that and the Savannah river, a distance of nearly 800 miles."

_T. triunguis_, the only African species, ranging from the Senegal and Congo into the Nile-system, but occurring also in Syria, is perhaps the largest of all Trionychidae, reaching a shell-length of almost 3 feet. The adults are olive-brownish above, the throat and under parts of the shell with round, white spots separated by a dark network. The young have whitish specks and spots.

_T. gangeticus_ and _T. hurum_ are the principal Indian species. The former is the larger of the two, with a shell of more than 2 feet in length; olive above, the young with fine black vermiculations; head with a black longitudinal streak from between the eyes to the nape, intersected by two or three chevron-shaped black streaks; under parts yellowish. _T. hurum_ is olive brown above {411}and below, in younger specimens with conspicuous, large, yellow spots on the sides of the head. The young are ornamented with two or three pairs of large round spots on the back, and the same applies to the beautiful young of the Burmese, _T. formosa_.

The three genera, _Cycloderma_ and _Cyclanorbis_ of Tropical Africa, and _Emyda_ of India, have a pair of cutaneous femoral valves or flaps on the plastron, beneath which the hind-limbs are withdrawn.

{412}CHAPTER X

DINOSAURIA–CROCODILIA

_SUB-CLASS V.–DINOSAURIA._

_Mesozoic, long-tailed, toothed reptiles, with distal ischiadic
symphysis, terrestrial limbs, large fixed quadrate bones and bifurcated
ribs._