1891.] W, L. Sclater — Notes on the Snakes in the Indian Museum. 249 



constant in scaling and coloui'. The points of distinction between 

 the two species ai'e as follows : 



In T. purjpureomaculatus the head scales are juxtaposed and convex 

 or keeled, the temporal scales are strongly keeled, the scales are in 

 25-27 rows and the colour is in spirit a porphyraceous blue ; in T. 

 gramineiis the head scales are small, smooth, and imbricate, the temporal 

 scales are also smooth, the scales are in 19 to 23 rows and the colour is 

 a uniform green. 



It is in most cases perfectly easy to distinguish these two snakes, 

 but there are in the Indian Museum some specimens which are interme- 

 diate in character, whether they are hybrids or not it ig difficult to say, 

 but as the two snakes inhabit approximately the same geographical area, 

 it is quite possible that this may be the case. 



Among the intermediate forms may be mentioned nine snakes from 

 Sibsagar in Assam (register no. 4015-28) which have the juxtaposed 

 convex head shields of T. purpureomaoulatus, but the smooth temporals 

 and 21 rows of scales of T. gramineus; again a snake (register no. 

 4109) from Moulmeiu has the convex head shields and keeled temporals 

 but only twenty-one rows of scales. 



Of T. furpureomaculatus the Museum contains examples from 

 Lower Bengal, and from various localities in Assam and Burma ; and 

 of T. gramineus, examples fi-om Simla, Sikhim, Assam, Burma and 

 Hongkong. / 



In the Islands of the Bay of Bengal, Preparis Isle, Cocos Isles, the 

 Andamans and Nicobars there are several different coloured varieties of 

 Pit vipers which, in my my opinion with one exception only, are better 

 referred to Tr. gramineus than to Tr. purp7ireomaculatus ; besides these 

 varieties there is a closely allied form, which is recognised by Boulenger 

 as a separate and distinct species ; this is Tr. cantoris of Blyth, of which 

 the Museum possesses a fair series, all from the Nicobars with one 

 exception, which is from the Andamans. 



The following is a list with brief descriptions of the various varieties 

 above mentioned. 



a. Preparis Island variety. 



Light brown above with darker dorsal and lateral spots ; ventrala 

 light coloured, marbled with brown, scales in 25 rows ; this form has 

 the characteristic juxtaposed convex head scales and keeled temporals, 

 and 1 hare considered it to be an insular variety of T. purpurea maculat us. 



b. Mottled variety. 



Brown above blotched with blue, below bluish with brown blotches, 

 scales in 23-25 rows, head scales as in T. gramineus. In the Indian 

 Museum there are a good number of snakes of this variety from the 

 Andaman Islands alone. 



