Cope.J loo [Dec. 19, 



A A. No preorbital plate. 



a. No suborbital plate. 



/5. Sympbyseal plates wide as, or wider than long. 

 Four superior labials ; caudal rings 17 A, alba L. 



/3/?. Sympliyseal plate longer than wide. 

 Superior labials 4 ; head short, wide ; tail smooth ; above spotted yellow 



and brown A. occidentalis Cope. 



Supei'ior labials 3 ; head acute ; tail smooth ; uniform above. 



A. dartcini D. & B. 

 Superior labials 3 ; head acute ; tail conical, with 18 rings ; several ter- 

 minal rings verj^ distinct and divided into prominent hard tubercles ; 



color uniform above A. trachura Cope. 



aa. A suborbital plate. 



/5. Two small labials below suborbital. 

 Four superior labials ; symphyseal and postsymphyseal narrow ; caudal 



rings 17, smooth A. angusttfrons Cope. 



/3/3. One large labial below suborbital. ' 

 Superior labials 4 ; tail smooth, with sixteen rings ; symphyseal and post- 

 symphyseal plates square ; unicolor above A. beniensis Cope. 



Superior labials 3 ; tail smooth with 26-8 annuli ; unicolor above. 



A. pretrei D. & B. 



aaa. Two suborbital plates. 

 Superior labials 3 ; symphyseal and postsymphyseal plates square ; tail 



with 29-33 smooth annuli ; spotted abpve A. faliginosa Linn, 



II. A supraorbital plate ; two frontonasals. 

 a. No preorbital (Zygaspis Cope). 



Several pairs of parietals and temporals ; inferior labiais 4. 



A. quadrifrons Peters. 



III. A supraorbital and preorbital plates ; frontonasals united. 



Gynisca Gray. 

 One pair of parietals and temporals ; inferior labials 3. .A. leucura D. &B. 



The Ampldsbcuna vermicularis D. & B. probably enters the above syn- 

 opsis near to the A. darwini, but I cannot learn all of its characters. It 

 is distinct from all the species of Division I, in having a more slender 

 body with more numerous annuli, viz., 232, according to Dumeril and 

 Bibron. I cannot now give the characters of the A. cainura Cope, as the 

 specimens are mislaid. 



In general appearance the AmpJiisbcena trackura. is a good deal like the 

 A. pretrei as figured in the zoology of Castelnau's journey in South 

 America. It also resembles in general the A. angustifrons from Buenos 

 Ayres. The head is elongate and the muzzle decurved and prominent. 

 The rostral plate is just visible from above. The frontonasals are each 

 longer than wide. The frontals form an oval which is just as wide as 

 long. The third superior labial reaches the ocular, and the row behind 

 these two plates consists of four scales to the frontal. Inferior labials 



