36 
NATURAL HISTORY. [[UPPER FLOOR. 
They are divided into several groups according to the 
structure of the tail, which, in the True Rattle-Snakes 
( Croioli ) ends in a rattle, formed by a series of horny joints, 
fitting one into the other, which the animal can shake at 
pleasure. There are in the Collection several species of 
this genus, and some detached rattles, to shew their struc¬ 
ture. The Tisiphone ( Tisiphone ) is much like the Rattle- 
Snake, but the tail ends in a small recurved spine: these 
are all peculiar to America. The other Snakes of this 
division have the tail simple at the end, and are found both 
in the Old and New World. The Cophias have the head 
covered with scales like those on the back, as the Fer de 
Lance of the French American Colonists. The Trigono - 
cephali have it covered with large shield-like plates. 
The next family, that of Vipers ( Viperidce , Case 6) have 
the same broad head as the Rattle-Snakes, but have no pit 
before the eyes. Amongst these the True Vipers ( Viper ee) 
are distinguished by the head being covered with scales 
like those on the back, and by the nostrils being very 
large. The Nose-horn Viper ( Coluber nasicornis ), has 
two horns on the end of the nose; the male of the Cerastes 
has a long horn-like scale over each eye, which being 
absent in the female, has caused the latter to be erro¬ 
neously described as a distinct species; the Puff Adder, 
or Short-tailed Viper ( Vipera injlata), is the most deadly 
snake of the Cape. The Adders ( Beri ) have the head 
covered with granular scales, and the nostrils moderate; 
and the Ammodyte has the end of the nose lengthened 
into a flexible horn. The Common Adder ( Coluber chef- 
sea') differs from these, by the crown of the head having 
three larger scales inserted amongst the smaller ones ; 
this is the only reptile found in Great Britain possessed of 
dangerously poisonous qualities. 
The Harmless Snakes, ( Ophidia Innocua , Cases 7—13,) 
on the contrary, have strong jaws, both furnished with 
one or more series of teeth. The head is of moderate 
size compared with the body, and its crown is covered 
with large regular shields. These species are, in general, 
innocent; a few have some of the upper lateral teeth 
rather larger than the rest, and grooved on the hinder 
edge, the groove communicating with a gland placed on 
