VIPER  . The vipers constitute a

family of Old-World poisonous snakes, with a pair of poisonous fangs in the maxillary bones, which are short and movable . The main anatomical features are described in the article SNAKES . In the present article only the Viperinae, namely those without an external pit between the eye and the nose, are described . Pit vipers, or Crotalinae, are treated under SNAKES, and those which are possessed of a rattle under RATTLESNAKE . The true vipers comprise about nine genera with some forty species, which can be distinguished as follows: Causus in Africa, and Azemiophis feae in Burma, are the only vipers which have the head covered with large symmetrical shields, while in the other genera the head shields are broken up into small shields, or into still more numerous scales . C. rhombeatus, common from the Gambia to the Cape . Atractaspis, small burrowing snakes in Africa, without post-frontal bones . Echis and Atheris have only one row of subcaudal shields . E. carinata, scarcely exceeding 20 in. in length, is very poisonous and easily overlooked on account of its light brown coloration, with pale spots and delicate markings on the keels of the scales of the back .