VIPER INE GROUP. 229 



to eighteen solid teeth in the maxilla, by the longer body, on the anterior part of 

 which the scales are imbricating, and by the presence of more or less distinct small 

 shields on the lower surface. 

 Black-Banded The black-banded sea-snake {Distira cyanocincta) may be taken 



sea-Snake. as an example of another large genus differing from the preceding in 

 that the fangs are followed in the maxilla by from four to ten solid teeth with 

 their front surface grooved. In these snakes the body is more or less elongated, 

 and generally has the scales on its front portion slightly overlapping, while the 

 under surface carries small shields. The figured species, which grows to a length 

 of 6 feet, is of a greenish olive above, with black transverse bars or rings, which 

 are sometimes connected by a longitudinal stripe on the under surface. This 

 snake ranges from the Persian Gulf to the Malay Archipelago and Japan, and is 

 one of the most abundant in the Indian seas. 



There are several points in which the sea-snakes differ from their land cousins 

 as regards habits, in addition to those already noticed. In the first place, the skin 

 is changed piecemeal, instead of entire ; the casting taking place at very frequent 

 intervals. Moreover, the tongue is very short, and only the extreme tips of its 

 two extremities are exserted through small notches on either side of the rostral 

 shield of the head, which is prolonged downwards so as to close the mouth. 

 When, however, these snakes are cast ashore and almost blinded by the unaccus- 

 tomed light, the tongue is used in the ordinary manner as a feeler. 



The Vipers. 



Family VlPERID^. 



Omitting mention of the small and unimportant family of harmless snakes 

 known as blunt-heads (Amblycephalidce), represented by two Oriental and two 

 tropical American genera, we pass to the viper family, which includes the 

 whole of the remaining members of the suborder. The distinction between a 

 colubrine and viperine snake is that in the latter the maxillre or hinder upper jaw- 

 bones are capable of being erected in a vertical plane at right angles to the 

 transverse bones, while in form they are short and thick, and they always carry 

 a single pair of large tubular fangs. All vipers are poisonous, and, so far as 

 known, produce living young ; while they are more or less nocturnal and terrestrial 

 in their habits, although a few ascend trees. The thick body, the flat and often 

 triangular head, the short and stumpy tail, the reduction of the maxillary teeth to 

 a single pair of fangs, and the vertical pupil of the eye, are all features dis- 

 tinguishing vipers as a whole from the poisonous colubrines ; but, as already 

 mentioned, it is frequently necessary to examine the structure of the skull itself 

 before any particular snake can be assigned to its proper serial position. That 

 the vipers form a highly specialised group is self-evident ; and Mr. Boulenger 

 believes them to be descended from the hind-fanged colubrines. The family is 

 divided into two groups, namely, the typical vipers of the Old World, which 

 attain their maximum development in Africa, and the American and Asiatic 

 pit- vipers. 



