214 THE SNAKES OF SOUTH AFRICA. 



Apart from the outward form, the Viperine snakes differ from 

 the Cohibrines in the formation of the upper jaw bones. The 

 maxillary bones in which the fangs are set are mobile, allowing 

 erection and depression of the poison fangs, which are large, 

 recurved and hollow, like the needle of a hypodermic syringe. 

 Behind the front fangs several duplicate sets of fangs arc stowed 

 away, graded in size down to mere specks. These are the Viper's 

 reserve set of weapons. H the front active pair of fangs be 

 shed or lost accidentally, the first pair of the reserve set take their 

 place, and become connected with the ducts communicating 

 with the poison glands. The supply of these reserve fangs is 

 indefinite. If those which are visible are removed, others develop. 



Numbers and Distribution. 

 There are about forty-two species of Vipers, and sixty-four 

 species of what are known as Pit-Vipers. The Vipers inhabit 

 Africa, Europe and Asia. The Pit-Vipers are unknown in Africa, 

 but occur all over Southern Asia, Central and South America. 

 The Rattle-snakes of America are Pit-Vipers. They are termed 

 such because of a pair of deep pits in the fore part of the head, 

 between the eyes and nostrils. The Pit-Vipers are classified 

 under the Sub-Family Crotalinse. In South Africa we have 

 ten species or kinds of Vipers. 



SYNOPSIS OF THE GENERA. 



Genus Causus. — Head distinct from neck, covered with symmetrical 

 shields ; nostril between two nasals and the internasal ; loreal 

 present ; eye moderate, with round pupil, separated from the 

 labials by suboculars. Scales smooth or keeled, with apical 

 pits, oblique on the sides, in 15 to 22 rows; ventrals rounded. 

 Tail: short, sub-caudals in two rows or single. 



Genus Bixis.^Head very distinct from neck, covered with small im- 

 bricate scales ; eye moderate or rather small, with vertical 

 pupil, separated from the labials by small scales ; nostrils 

 directed upwards, or upwards and outwards, pierced in a single 

 or divided nasal, with a deep pit or pocket above, closed by a 

 valvular, crcsccntric supranasal. Postfrontal bone very large, 

 in contact with the ectoptergoid, which has an outer, hook- 

 shaped process. Scales keeled, with apical pits, in 22 to 41 rows ; 

 lateral scales in some species slightly oblique ; ventrals rounded. 

 Tail very short ; sub-caudals in two rows. 

 Genus Atractaspis. — Poison fangs enormously developed ; a few teeth 

 on the palatines, none of the pterygoids. Head small, not dis- 

 tinct from neck, covered with large symmetrical shields. Nostril 

 between two nasals ; no loreal. ]£ye minute, with round pupil. 

 Postfrontal bone absent. Body cylindrical. Scales smooth, 

 without pits, in 17 to 37 rows ; ventrals rounded. Tail short. 



