SIDE-NECKED TORTOISES. 
93 
Nocturnal and carnivorous in their habits, the snake-necked tortoises appear 
to agree in their general mode of life with the majority of fresh-water species. 
During the daytime they are generally to be found lying asleep on some dry spot 
near the water, with the neck bent on one side, and the head, like the limbs and 
tail, retracted within the margins of the carapace. When disturbed, the head and 
neck are, however, shot out with marvellous rapidity, reminding the observer of the 
sudden dart of a snake. 
Australian Long- In Australia and New Guinea the place of the preceding group 
Necked Tortoises. j s taken by another genus of long-necked tortoises, technically known 
as Chelodina, the members of which may be recognised by the presence of a 
normally placed nuchal shield 
on the carapace, coupled with 
the circumstance that the inter- 
gular shield of the plastron, 
instead of being placed between 
the gulars, as in the figure on 
p. 89, is situated behind the 
latter, which consequently meet 
in the middle line. The ver¬ 
tebral horny shields are longer 
than broad, and the whole of 
the shields remarkable for their 
extreme thinness. On remov¬ 
ing the latter from the carapace, 
it will be found that, owing to 
the absence of neural bones 
all the pairs of costal bones 
meet in the middle line,—a peculiarity shared with one American, and two other 
Australian genera of the family. There are four species of these long-necked 
tortoises, three of which are found in Australia, while the fourth is Papuan. 
In addition to the foregoing, there are four other genera 
belonging to the family under consideration, collectively distinguished 
by their shorter necks, the length of which is inferior to that of the back. Of 
these the American Rhinemys, Hydraspis, and Platemys are characterised by the 
narrow anterior extremity of the lower jaw, and by the first vertebral shield of 
the carapace being wider than either of the others. The second of these genera, of 
which a member is represented in the accompanying figure, is by far the most 
numerous in species; and is noteworthy on account of being represented by a 
fossil species in the Eocene deposits of India. The third genus differs from the 
other two in the absence of neural bones to the carapace. On the other hand, the 
two Australian genera —Emydura and Elseya ,—both of which present the feature 
last mentioned, are distinguished by the broad anterior extremity of the lower 
jaw, and by the first vertebral shield of the carapace not exceeding the others 
AN AMERICAN SIDE-NECKED TORTOISE ( Hydraspis ). 
Other Genera. 
in size. 
Greaved 
Tortoises. 
The tortoises which may be conveniently designated by a 
translation of their scientific title ( Podocnemis )—so named on account 
