On Milos, Dr. de Bedriaga observed this much-dreaded snake, the bite of which is probably as bad as that of its Indian ally, the Daboia, _V. russelli_, to occur frequently in gardens, and to crawl about near houses in villages after sunset. The same observer has noted a sort of valvular closing of the nostril through raising of the posterior part of the nasal shield when the snake prepares to strike.
The food consists principally of mammals up to the size of a rabbit.
_Reproduction._--According to Doumergue's observations in Algeria, the young, up to thirteen in number, are born in May and June.
Head distinct from neck, its upper surface covered with large shields, as in the normal _Colubridæ_; a loreal pit; eye moderate or small, with vertical pupil. Body moderately elongate or short. Scales keeled (or smooth), with apical pits. Tail moderate or short.
This genus is distributed over nearly the whole of Asia, the eastern parts of the United States of America, and Mexico and Central America. One of the Asiatic species just penetrates into South-Eastern Europe, and is the sole representative of the Crotalinæ in this part of the world.
28. ANCISTRODON HALYS, Pallas Pallas's Pit-Viper
_Form._--Moderately elongate. Head subtriangular, flat or slightly concave above, swollen in the temporal region, very distinct from neck; snout rounded or obtusely pointed, slightly turned up at the end, with obtuse canthus and vertical or slightly oblique loreal region; eye rather small. Tail seven to eight and a half times in the total length.
_Head-Shields._--Rostral as deep as broad or slightly broader than deep, just visible from above. A pair of internasals and a pair of larger prefrontals. Frontal as broad as the supraocular, as long as or a little longer than its distance from the end of the snout, as long as or a little shorter than the rather short parietals. Supraocular extending beyond the vertical of the posterior border of the eye. Loreal pit between three shields, separated from the labials. Nostril between two nasals, the posterior of which is separated from the upper preocular by a loreal. Two preoculars, one or two postoculars, and a subocular. Three large lower temporals, anterior largest. Upper labials seven or eight, third and fourth largest, third entering the eye. A pair of small chin-shields.