14 INTRODUCTION 



Snakes are covered with epidermal folds in the form 

 of scales and shields, the shape and arrangement of 

 which affords important characters for their classifica- 

 tion. Dermal ossifications are absent. 



The scales on the body are usually elliptic or 

 lanceolate and imbricate, forming straight longitudinal 

 and oblique transverse series, and they are replaced 

 on the belly and under the tail by transverse shields 

 mostly corresponding in number with the series of 

 scales, and also with the vertebrae. The body of the 

 Typhlopidae and Glauconiidse is uniformly covered 

 with polished, closely adherent, rounded, overlapping, 

 sub-equal scales, without even an indication of ven- 

 tral shields. Jn some of the Acrochordinae, aberrant 

 aquatic Colubrids, the scaling consists, above and 

 beneath, of small juxtaposed, sometimes spinose 

 granules, the skin being suggestive of the shagreen of 

 sharks. In the marine snakes of the subfamily 

 Hydrophiinae, the ventral shields are often absent or 

 merely indicated, and the scales are mostly juxtaposed 

 or feebly imbricate, sometimes tetragonal or hexag- 

 onal, and occasionally studded with spinose tubercles. 

 In the more typical Ophidia the imbricate scales may 

 be long and narrow or short and broad, with every 

 intermediate step between the two extremes; smooth 

 or furnished with a longitudinal ridge or keel, or even 

 several keels ; nearly equal in size or with the median 

 or outer series more or less enlarged, the longitudinal 

 series in odd, rarely in even number ; instead of run- 



