50 REPTILES. 



Fam. III. NATRICIDiE. 



Body moderate, rather stout, generally depressed, with flat 

 belly, sometimes rounded. Tail moderate or short, in one genus 

 elongate, more or less distinct from trunk, tapering. Head 

 generally depressed, broad, distinct from neck, with rounded 

 muzzle, in Heterodon with pyramidal rostral. Cleft of mouth deep. 

 Eye moderate or large, pupil round. Nostril between two nasals, 

 in Tomodon only one nasal ; number of oculars variable. Scales 

 generally with strong keels, but often smooth, generally in nine- 

 teen rows. Ventral plates without lateral keels. Posterior max- 

 illary teeth longest, in a few species equal, in some grooved. 

 Freshwater Snakes. 



Xenodon, Tropidouotus, Heterodon, Schlegel. Ischnognathus, 

 Syncranteriens, gg., Diacranteriens, gg., Dum. Sf Bibr. 



Synopsis of the Genera. 



1 . Grayia. Scales smooth, rounded, hardly imbricate ; five 



very large temple-shields ; teeth equal, smooth. West 

 Africa. 



2. Tomodon. Scales smooth, rhomboid, much imbricate ; pos- 



terior maxillary tooth very long, grooved. South America ; 

 India. 



.'$. Xenodon. Head very broad, short ; anterior frontals broad, 

 rounded in front ; posterior maxillary tooth longest, and 

 separated by an interspace. South America ; India. 



4. Tropidonotus. Scales keeled ; muzzle rather narrow and 



pointed in front ; anterior frontals narrow, pointed in front ; 

 one loreal ; posterior maxillary tooth longest (in one species 

 short), generally in a continuous row with the other ones. 

 Almost every part of the globe. 



5. Ischnognathus. Scales keeled ; loreal none; teeth equal, 



smooth. North America. 



H. Heterodon. Rostral with a sharp ridge above ; neck dis- 

 tensible. America ; Madagascar. 



1. Grayia, G'dnther. 



Body rather stout, cylindrical, belly rounded; tail long, 

 rounded, tapering, not distinct from trunk ; head depressed, with 

 Hat crown and rather short and rounded muzzle, distinct from 



