AFRICAN SNAKES. 



195 



such difficulties to the uninitiated in herpetology. For instance, 

 a. beginner may be in doubt whether the snake before him is an 

 Aglyphous, an Opisthoglyphous or a Proteroglyphous Colubrid, 

 or even a Viperid. In that case, confining his attention to the 

 external characters, he may have to work through the four keys 

 to the genera of the above-named groups; but these keys have 

 been so constructed that he cannot alight on any name but the 

 one he is seeking. To give an example, supposing he has before 

 him a Causus rhombeattos, and, not having looked at the teeth, 

 has no idea to what group it belongs. He will first try Colubriclse 

 aglyphse. His specimen will fall under division I. A. of the key, 

 but will be excluded from any further definition. Passing on to 

 the Oolubridee opisthoglyphse he will reach division II. B, and no 

 further. The presence of a loreal shield in the snake before 

 him will rule it out of the Colubridpe proteroglyplne. Then trying 

 the last key, Viperida?, he will at once alight on Causus, and 

 further on on Causus rhombeatus. 



No further glossary is needed than the outline figures here ap- 

 pended to this list. I will only add that in giving the number of 

 subcauclal shields, if in pairs, each pair is reckoned as one, and 

 the conical or spine-like shield which caps the end of the tail is 

 not included. 



Text-figure 2. 



ventrals scales ( 15 rows) ventrals scales ( 21 raws) 



A B 



Scaling of thickest part of body. 

 A. G-astropyxis smaragclina, with keeled scales and bicarinate ventral shields. 

 13. Dipsadomorphus blandingii, with oblique scales and enlarged vertebrals. 



Synopsis of the Families. 



I. Worm-like, with small inferior mouth, eyes hidden or visible under the head- 



shields, and body covered with uniform imbricate scales above and beneath. 

 Ocular shield not bordering the mouth; tail not or but little 



longer than broad Typhlopice. 



Ocular shield bordering the mouth ; tail at least three times as 



long as broad Glauconiibj]:. 



II. Mouth large, eyes distinct, body with enlarged shields beneath. 

 Ventral shields much narrower than the body; supraocular, if 



distinct, broken up into two or more shields Boid^;. 



Ventral shields at least nearly as broad as the body ; supraocular, 

 if present, single ; poison-fangs, if present, not in a very large 

 sheath Colubkid.e. 



Ventral shields at least nearly as broad as the body ; large poison- 

 fangs in a very large sheath below the eye , Viperid.t;. 



