SNAKES OF CEYLON. 91 



and about haK the ultimate row. The ultimate row is 

 enlarged, and the breadth of its scales subequal to their 

 length. The rows are 19 two heads-lengths behind the head 

 (except in punctulatus, 17), 19 at midbody, and later reduce 

 to 17 by an absorption of the fourth row above the ventrals 

 (except punctulatus, where it reduces to 15). 



Dentition. — Prom the skulls of five species in my collection, 

 viz., piscator, tessellatus, xenura, venningi, and modestus. 



Maxillary : 21 to 29 ; syncranterian, anododont, cory- 

 phodont. Palatine : Anododont, isodont. Pterygoid : Ano- 

 dodont, isodont, except the last three or four which reduce 

 in size. Mandibular : Anododont, isodont, or feebly kumat- 

 odont. 



Distribution. — Thirteen out of the twenty-four species 

 recognized by Boulenger are American, three (one dubiously) 

 African, seven Asian, and one European. 



Nerodia (tbopidonottjs) piscator* Schneider. 

 (Latin " piscator," a fisher.) 



The Chequered Keelback. 



Tamil : " Tanni pambu " (water snake) ; Singhalese : " Diya 

 polonga " (water snake). (WiUey.) 



Synonymy. — Hydrus piscator, H. palustris, Coluber 

 anastomosatus, C. umbralus, C. braminus, C. mortuarius, 

 C. dora, C. hippus, 0. bengalensis, C. rectangulus, Enhydris 

 piscator, Amphiesma flavipunctatum, Tropidonotus melano- 

 zostus, T. mortuarius, T. quincunciatus, T. umhratus, T. 

 tytleri, T. flavipunctatus, T. striolatus. 



* Boulenger in his catalogue (Vol. I., p. 232) concedes to this 

 the rank of a species under the name Tropidonotus aaperrimua, on the 

 grounds that in this form all the costal rows are keeledexcept the last, 

 whereas in T. piscator two or three rows are not keeled. I have 

 examinedmanyhundredsof Indian piscator, and find that the number 

 of rows not keeled is variable. I have also examined several of the 

 Ceylon form asperrimus most critically, beside the Indian piscator, 

 and cannot discover any constant character whereby the two can be 

 separated. Asperrimus, however, I consider a distinct colour variety 

 of piscator peculiar to Ceylon, an insular form comparable to the 

 Andaman variety tytleri of Blyth. To those who follow Boulenger 

 the snake should be called Tropidonotus asperrimus. 



