186 



JOURNAL, R.A.S. (CEYLON). [VOL. XL. 



imbricate and sometimes tesselated, with every gradation 

 between the two extremes ; in the curious Ghersydrus (No. 

 34) the scales are merely rough warts thickly set over the 

 head and body. 



The Head Shields. 



The description of the head shields of Zamenis mucosus 

 under letter a is a very full one : all the most important 

 characters are given, and when a snake differs from this 

 species in any of these characters I consider that these 

 differences ought to be expressed by a new letter. There 

 appear to me to be thirteen quite distinct types of head 

 shields in Ceylon snakes, expressed by the letters a to n. 

 By means of the index figures it would be possible to extend 

 these descriptions to any length. Following Dr. Gunther, 

 No. 24, Z. mucosus, a 1 , might read thus : "Rostral broader than 

 high ; two nasals ; three loreals • upper labials all reaching the 

 labial margin ; internasals more Jian half the size of anterior 

 frontals, pointed in front ; one prae-ocular reaching to the 

 upper surface of the head ; frontal five-sided ; basal margin 

 shorter than lateral, which are slightly concave ; posterior 

 margins converging to a point ; supra-ocular projecting : 



Explanation of the Plate. 



A = Head Shields of the a type. 



R. 





rostral. 



PstOC.= 



post-oculars. 



IN. 





internasal. 



T. = 



temporals. 



PrF. 





prae-frontals. 



UL. = 



upper labials. 



F. 





frontal. 



LL. = 



lower labials. 



S.O. 





supra-ocular. 



C. = 



chin shields. 



P. 





parietal. 



I. = 



ventral and caudal 



N 





nasals. 





shields of the a 1 type. 



L. 





loreal. 



IT. = 



ventral and caudal 



OC. 





pre-oculars. 





shields of the d type. 



Types L, M, an d N are n °t given, as they can be easily understood 

 from the description. Type G is much like F, but the front margin 

 of the orbit is formed by the prae-frontals. 



