REPTILES AND .BATRACHIANS FROM SIAM AND INDO-CHINA. 213 



the angle of the jaw, with fine longitudinal folds and an alteration 

 in the character of the skin at that point. This did not appear in 

 R. mortenseni. 



Since then I have examined a further large series (over 50 

 examples) of nigrovittata from various parts of Siam. The collection 

 moreover includes many full grown males, considerably larger than 

 any previously available for examination, and quite as large as the 

 R. mortenseni from Koh Chang. 



In all the specimens of nigrovittata from Peninsular Siam 

 (largest not over 55 mm. from snout to vent), and in most of those 

 of equal size from N. and N. E. Siam, this condition of external vocal 

 vesicles is evident, but in the larger specimens (65 - 70 mm.) the 

 pigmentation has disappeared, and the skin has resumed its normal 

 colour. The folds, however, still remain ; they are more .strongly 

 marked in some than in others. 



I have never seen any immature males of R. mortenseni ; and 

 in the few adults I have examined the skin of the throat appears 

 unchanged. 



Tadpoles obtained on Koh Chang, where mortenseni appears 

 to be the only frog of this group in existence, do not differ from 

 tadpoles of R. nigrovittata which I have obtained in other parts of 

 Siam. 



The other points of distinction between the two species which 

 I had relied on, namely, the slight difference in the finger tips and 

 the longer leg, disappear with the larger amount of material 

 examined. 



It would seem correct therefore, to unite mortenseni with 

 nigrovittata, and, as regards the question of vocal sacs to describe 

 the species as having internal or feebly developed external ones. 



Although my series from different parts of the country inter- 

 grade completely with each other it is possible to correlate certain 

 broad variations with geographical areas. 



(1) From Peninsular Siam. Presuming my specimens to 

 be fully grown, this is the smallest form. Its length from snout to 

 vent does not exceed 55 mm. The vocal vesicles are feebly developed 



VOL. IV, NO. 4, 1922, 



