viii INTRODUCTION. 



the anterior in the latter generally ranging. Thus, when the ver- 

 tical plate is very short, the anteorbital is also short or wanting 

 entirely, and the same relation holds good between the loral and 

 postfrontals. 



The specimen whose measurements are first given, unless stated to 

 the contrary, has served as the type of the description, and the first 

 mentioned species is to be considered as the type of the genus. 



Of the five numbers given at the end of the descriptions, the first 

 indicates the number of the abdominal scutellae from chin to anus. 

 The second is that of the pairs of subcaudal scutellae ; the third, the 

 dorsal rows or the number of rows of scales around the body (ex- 

 cluding the abdominal series). The fourth number shows the entire 

 length of the animal, and the fifth the length of the tail, in English 

 inches. 



In referring to the dorsal rows, the exterior one, or that next the 

 scutellae, is considered to be the first, unless the contrary is stated. 



When there are two numbers separated by the symbol at the be- 

 ginning of the measurements, the first indicates the number of entire 

 abdominal scutellae, the latter of those that are bifid or divided. The 

 subcaudal scutellae are to be considei'ed as divided or in pairs, unless 

 mentioned to the contrary. 



In enumerating the number of labial plates, those on one side of 

 the jaws only are to be understood, and the terminal and median one 

 on the symphysis of the upper and lower maxillaries is never in- 

 cluded. On the upper jaw that plate is at the end of the snout, and 

 is the rostral. 



The descriptions are all based on specimens preserved in alcohol, 

 unless otherwise stated. 



