PYTHONS AND BOAS. 
1S9 
head usually has a more or less distinct streak behind the eye; while the under¬ 
parts are pale olive or yellowish, more or less spotted with brown or black. 
Dog-Headed Closely allied to the last, the live species of the genus Corallus 
Tree-Boa. are distinguished by having deep pits in the labial shields of both 
the upper and lower lips. The body is compressed, with small smooth scales, and 
the prehensile tail is either short or more or less elongated. This genus has a 
somewhat remarkable distribution, four of its representatives being inhabitants 
of tropical America, while the fifth ( C. madagascariensis). which is distinguished 
from the rest by the shortness of its tail, is restricted to Madagascar. The 
dog-headed tree-boa (C. caninus) is a native of the Guianas and Brazil, and 
usually attains a length of some 5 feet, although it may be considerably larger. 
It belongs to a group of two American species distinguished from the other kinds 
inhabiting the same countries by the relatively shorter tail, which has only from 
sixty-four to eighty-two shields on its inferior surface; whereas in the true 
tree-boa (C. hortnlanus), and another species, there are at least a hundred of 
these shields. The species here figured is specially characterised by having the 
scales arranged in sixty-one or seventy-one rows, and by the number of shields on 
the under surface of the body ranging from one hundred and eighty-eight to two 
hundred and nineteen, while those on the tail vary from sixty-four to seventy-nine. 
In colour this snake is decidedly handsome, the upper-parts of the adult being 
bright green, ornamented with irregular spots and crossbars of white, and the 
under-parts bright yellow. In the young the ground-colour is yellowish, and the 
white markings are edged with dark green or purplish black. Most abundant 
in the neighbourhood of the Amazons, this species becomes more rare in Guiana, 
while southwards it likewise diminishes in numbers in lower Brazil. Feeding 
principally upon birds, the dog-headed boa is an excellent swimmer, and has been 
observed both in the Rio Negro and in the salt-water of the beautiful harbour 
of Rio de Janeiro. Although it frequently visits the huts of the Brazilian negroes 
in search of prey, it does not appear that this snake ever voluntarily attacks 
human beings. If, however, it is driven to bay and unable to escape, it is capable 
of inflicting very severe bites with its long front teeth, such wounds being- 
difficult to heal. 
Keeled A third genus of tree-boas ( Enygrus ) is distinguished from both 
Tree-Boas, the preceding by the scales having distinct keels ; the labial shields 
of the head being devoid of pits, and the tail short and prehensile, with a single 
row of shields on its inferior surface. This genus is represented by four species 
inhabiting the Moluccas, the Papuan region, and Polynesia. 
This gigantic snake is the sole member of a group of several 
Anaconda. g enera> distinguished from the tree-boas by the teeth gradually 
decreasing in size from the front to the back of the jaws without any marked 
enlargement of those in the fore-part. Merely mentioning the allied tropical 
American genera, Trachyboa, Ungalia, and Ungaliophis, the first and last of which 
are each represented only by a single species, we may observe that the anaconda 
is specially distinguished as a genus by the large size of the rostral shield of 
the head, behind which one pair of the nasals come in contact with one another 
in the middle line, and by the very small size of the smooth scales of the body. 
