Quadrate longer than supratemporal; maxillary much longer than quadrate, nearly straight in front of prefrontal; a large vacuity between the frontal bones and the basisphenoid _Coelopeltis._ Quadrate not longer than supratemporal; maxillary little longer than quadrate, strongly curved in front of prefrontal _Macroprotodon._ Quadrate longer than supratemporal; maxillary little longer than quadrate, nearly straight in front of prefrontal _Tarbophis._ [Illustration: FIG. 10--SKULL OF _Vipera lebetina_. (From British Museum Catalogue of Snakes) Lettering of the bones as in Fig. 3] 2. Maxillary much abbreviated and erectile; supratemporal not half as long as skull; mandible much longer than skull; basioccipital with a strong process. Maxillary bone solid _Vipera._ Maxillary bone hollowed out _Ancistrodon._ The vertebræ number 130 to 500--in the European forms 147 (_Vipera ursinii_) to 330 (_Coluber leopardinus_). The vertebral column consists of an atlas (composed of two vertebræ) without ribs; numerous precaudal vertebræ, all of which, except the first or first three, bear long, movable, curved ribs with a small posterior tubercle at the base, the last of these ribs sometimes forked; two to ten so-called "lumbar vertebræ" without ribs, but with bifurcate transverse processes (lymphapophyses) enclosing the lymphatic vessels; and a number of ribless caudal vertebræ with simple transverse processes. When bifid, the ribs or transverse processes have the branches regularly superposed.