SNAKES OF CEYLOK. 83 



three -fourths that between the prefrontals, and three -fifths to 

 three-fourths the internaso -prefrontals. The suture between 

 the prefrontals about three -fourths, to subequal to the 

 prefronto -frontal. Fronto -supraocular sutures twice or 

 nearly twice the fronto -parietals. Supraoculars nearly as 

 long as the frontal, and half to three -fourths the breadth of 

 the frontal along a line connecting the centres of the eyes. 

 Nasals : Two. Lor ml : About half the length of the 

 nasals. Three supralabials touch the eye. 



Costals : Longer than broad, rectiform, smooth, and 

 without apical pits or facets. Vertebral row not enlarged. 

 Ultimate row enlarged, and the scales as long as broad. Rows 

 17 to 19, remaining the same in the whole body length. 

 Ventrals: Rounded. Anal: Divided. Subcaudals: Divided. 

 The supracaudal rows are in even numbers. 



Distribution. — Most of the ten species are Asian. Two 

 are American, two Madagascarian, and one peculiar to the 

 Comoro Islands. Of the five Asian species, four belong to 

 the Indo-Malay fauna, and one is Indian. This last, viz., sub- 

 punctatus, occurs in Ceylon. 



Dentition. — The teeth in all the jaws are very numerous, 

 and extremely small. Maxillary : 30 to 50 isodont, and 

 syncranterian ; Palatine, pterygoid, and mandibular : Isodont 

 and anododont. The teeth in the species of this genus are 

 peculiar. In most snakes teeth are being continually shed, 

 and replaced, and at any given time if the jaws are dissected 

 out, every alternate tooth will be found to be loose. In 

 consequence, it is almost impossible to prepare any of the 

 jaws with a perfect set. In this genus, on the contrary, 

 practically all the teeth at any given time are found firmly 

 ankylosed, and it is easy to prepare an almost perfect set in 

 spite of their number and small size. Further, with very 

 rare exceptions, snake's teeth, whether moderately or strongly 

 compressed, end in a needle, or dagger point. In Polyodon- 

 tophis the teeth are moderately compressed, and end in a 

 sharp edge somewhat like a chisel, only it is rounded instead 

 of being straight. The edge is parallel to the jaw. A third 

 distinction lies in the curious fact that the chisel-edge is 

 always discoloured, being tinctured brownish. 



