J 86 A new genus of Serpents, ^r. 



1. Heterodon NIGER. P. de Beauv.* 

 Hognose Snake, Siircadmg Adder. 



Abdominal scuta, from 135 to 146. 



Subcaudal scutella, from 52 to 55, 



Whole length 34 to 36 mches. 



Of which the tail is 5^ to 5f inch. 



Head, to the extremity of os articulare li inch. 



Of which the larger plates cover —^ inch. 

 The head is nearly of the same diameter with the neck ; so 

 that when we are not acquainted with the skeleton of the head 

 we cannot determine where the head terminates and the neck 

 commences, but the skeleton shows that the head terminates 

 with the large plates; so that, in the individual, the dimensions 

 of which have been given, the os occlpitis lies exactly under 

 the posterior edge of the plates ; and the head being about an 

 inch, and the tympana half an inch long, the latter projects half 

 an inch behind the former. 



The head is covered with ten plates. The upper lip, or tip 

 of the muzzle, is flat, erect, running, keel-shaped, backwards ; 

 upon which follows a small elongated oval plate, forming, with 

 the keel mentioned, an irregular tetrahedron. The two first 

 plates, having an irregular triangular form, are placed on each 

 side of this tetrahedron : they constitute part of the edge of the 

 nostrils, and join to the three following ; of which the middle 

 one is the small oval plate already mentioned ; and the two 

 side ones, having a very irregular trapezoidal form, compose 

 the upper edge of the nostrils, and extend as far as the upper 

 part of the small oval plate. Next follow two large irregular 



* As all the descriptions which have come under my observation are 

 very incorrect, and in many parts deficient, particularly in the description 

 of the head, which also is badly represented by Daudin, (pi. lx, fig. 28) 

 \ suppose a more correct description will be acceptable to the herpetolo- 

 gist who does not inhabit the places where these reptiles are found. 



