00 SNAKES OF CEYLON. 



Sub-genus Nerodia. 



Maxillary teeth, not more than 30, the hinder gradually 

 enlarged. Eyes rather small, and like the nostrils, directed 

 upwards and outwards ; internasal shields usually much 

 narrowed in front. 



Sub -genus Amphiesma. 



Maxillary teeth not more than 30, last two or three abruptly 

 enlarged. 



Sub -genus Macropophis. 



Maxillary teeth 35 to 40, posterior but slightly enlarged. 

 Eye very large. Body very slender. 



Only two of these divisions, viz., Nerodia and Amphiesma 

 are represented in Ceylon. 



Genus NERODIA.* 



(Greek " neros " wet, from the sub-aquatic habit of 

 many of the species.) 



General Characters. — " Maxillary teeth not more than 30, 

 the hinder gradually enlarged. Eyes rather small, and like 

 the nostrils, directed upwards and outwards ; internasal 

 shields usually much narrowed in front" (Boulenger). 



Poison. — Non-poisonous. 



Lepidosis. — I notice a feature in the scales of many species 

 allied to these that has escaped the observation of previous 

 herpetologists, and which may considerably assist in the 

 grouping of these closely allied forms. I allude to the apical 

 emargination of the costals. (Vide figure 28.) 



In the species of Nerodia as now constituted, I find the 

 emargination present in tessellatus and xenura of those 

 known to me, but it is absent in piscator, venningi, and 

 punctulatus. 



In all the species known to me the scales are longer than 

 broad, rectiform, and keeled. The vertebral row is not 

 enlarged, the breadth of its scales is about half their length, 



* The differences between Nerodia, and Tropidonotus are not so 

 marked as those between Amphiesma and Tropidonotus, so that the 

 claims of Nerodia for Generic rank are not so great as Amphiesma, 



