EXPLANATION OF TERMS USED. 



Tub vertical plate (u) is the central one in the middle of the head above, having 

 on each side of it the superciliarles (s,s), which form the upper part of the 

 orbit. The two plates behind the vertical are the occipitals (_o,o); the pair in 

 front of it, the postfrontals (p,/). The prefrontals or anterior frontals (a,/) 

 are situated in front of the postfrontals; and anterior to these, and terminating 

 the snout, is the rostral (r). The plates immediately in front of the eye are the 

 anteorhitals (a) : those behind it are the postorKtals (p,o). In advance of the 

 anteorbital is the hral (to) ; between which and the rostral are the two nasals 

 (n), with the nostril between them. The upper and lower labials (i,?) margin 

 the upper and lower jaws : only one of each series is marked. The temporal 

 shields (i) are situated between the upper labials and the occipitals. The infra- 

 maxillary or mental scutellse or shields are just within the lower labials : these 

 cannot be shown in the figure. 



The arrangement on the top of the head of one rostral, two pairs of frontals, 

 one vertical with one superciliary on each side, and one pair of occipitals we 

 have considered as typical or normal, from \yhich but few of the genera described 

 vary. Sometimes one plate occupies the place of the two prefrontals; and in 

 some genera a second median plate is seen between the rostral, frontals and 

 vertical. On the side of the head we have sometimes but one nasal, and some- 

 times either the loral or the anteorhitals may be wanting. Where the latter 

 condition exists, it is sometimes diiflcult to determine which plate has dis- 

 appeared. A clue is to be found in the shape of the remaining plate : if this be 

 longitudinal, it is probably the loral; if vertical, or divided into two or more, 

 one above the other, it is to be considered as anteorbital. The loral belongs to 

 the postfrontals, and the anteorbital to the vertical, the posterior edges in the 

 former and the anterior in the latter generally ranging. Thus when the vertical 

 plate is very short, the anteorbital is also short or wanting entirely; and the 

 same relation holds good between the loral nnd postfrontals. 



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

 the number of the abdominal scutellse from chin to anus; the second is that of 

 the pairs of subcaudal scutellse; the third, the dorsal rows, or the number of 

 rows of scales around the body (excluding the abdominal series) : the fourth 

 number shows the entire length of the animal; and the fifth, the length of the 

 tail in english inches. 



