SIDE-NECKED TORTOISES. 
95 
separated from one another in the middle line. The toes are broadly webbed, and 
the tail is remarkable for its extreme shortness. 
The figured species, which inhabits tropical South America to the eastwards 
of the Andes, and is extremely abundant in the upper part of the Amazonian 
system, has the shell expanded posteriorly, and much depressed in the adult, 
although at an earlier stage it has a roof-like form. The chin is furnished with 
two small wart-like appendages; and the hind-foot characterised by the presence 
of two very large shields on its outer side. In colour, the upper shell is brown or 
olive, with darker markings, while the plastron is yellowish, spotted with brown ; 
the young being olive above and yellow beneath, with some yellow spots on the 
head. All the other members of the genus are of greatly inferior dimensions; a 
second Amazonian species (P. sextuberculata), having a shell of scarcely more than 
a foot in length, and being distinguished from its larger relative by the presence 
of only a single wattle on the chin. 
The best account of the habits of these tortoises is the one given by Humboldt, 
who speaks of the large species by its native name of arran. On the Orinoco, 
according to this account, the period of egg-laying coincides with that of the 
lowest level of the waters of the river, or from the end of January till the latter 
part of March. During January the tortoises collect in troops, which soon leave 
the water to bask on the warm banks of sand exposed by the lowering of the 
river. Throughout February they may be found on such banks during the greater 
part of the day; but early in March the several troops collect in larger bodies, and 
then make their way to the comparatively few islands where the eggs are 
habitually deposited. At this time, shortly before the egg-laying commences, 
thousands of the tortoises may be seen arranged in long strings around the shores 
of the islands in question, stretching out their necks, and holding their necks 
above water, in order to see whether there is anything to prevent their landing in 
safety. As the creatures are exceedingly timid, and especially averse to the 
presence of human beings or boats, the Indians, to whom the harvest of tortoise- 
eggs is of the utmost importance, take every precaution to prevent them being 
disturbed, posting sentinels at intervals along the banks, and warning all passing 
boats to keep in the middle of the river. When the tortoises have landed, the 
laying of the eggs takes place at night, and begins soon after sunset; the females 
digging holes of some three feet in diameter and two feet in depth, by the aid of 
their powerful hind-limbs. So great is the contention for space, that one tortoise 
will frequently make use of a pit dug by a neighbour, and in which one set of eggs 
has already been deposited, although not yet covered over with sand; two layers 
of eggs thus occupying one area. The crowding and jostling of the reptiles 
necessarily leads to an immense number of eggs being broken, which is estimated 
at a fifth of the whole; the contents of the fractured shells in many places 
cementing the loose sand into a coherent mass. The number of tortoises on the 
shore during the night being so large, many of them are unable to complete the 
work of egg-laying before dawn; and these belated individuals become quite 
insensible to danger, continuing there even in the presence of the Indians, who 
repair to the spot at an early hour. 
The great assemblage of these Chelonians takes place on one particular island 
