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 



