28 



The ventral shields are narrow at their first appearance 

 between the chin shields ; the first one or two are often 

 bifid, and as many as ten to twenty rows of ordinary scales 

 often intervene before they begin. (All the scales which 

 intervene between the last pair of geneial shields, and the 

 first undivided ventral are called gular scales). The ventrals 

 are absent, rudimentary or narrow in the burrowing snakes, 

 the grovelling snakes, the pythons and the sea-snakes, 

 whilst they are most developed in tree-snakes and others 

 of active habits. In these latter they become broad, turned 

 up at the sides, and often have on each side a lateral keel 

 so well developed as nearly to divide them into three 

 sections. The last of the ventral series is the anal shield ; 

 it is generally bifid, and this character, when it occurs, is 

 very regular. Still more regular is the single or double 

 condition of the subcaudal shields, scutellce ; they are gene- 

 rally double, being divided down the centre by a zigzag line. 



To this rule the following are exceptions : — 

 Families. Genera. 



^ , .7 f Aspidui'a, 



Calamaridce - rr 7 ' 



( Haplocercus. 



Lycodontidcc Cercaspis. 



AmhlycephalidcV' ... Amhlycephcdus. 



ErycuK^ - /> 7 7. 



( (jongyloplnH. 



arus. 



i Bung 



J^lmdce....'. < Megcerophis, | ^^^ 



[^ Opkiopliagiis, 3 



Vipcridoe Echis. 



In OpMophagiis, and occasionally in Naga, the last few 

 ventrals may be double, though the anal is always single. 



The number of ventrals and subcaudals corresponds close- 

 Iv with that of (he vertebr?e. The number is variable, not 



