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



V 5Q _ 79 - shows that there are from one hundred and 

 twenty-five to one hundred and sixty-one ventral shields, 

 and from fifty to seventy-nine sub-caudals, in the 

 species. 



Dr. Gunther uses the formula 1 + 2, 2 + 2, &c, to express 

 the arrangement of the temporal shields, meaning that 

 there is one temporal behind the eye, followed by two 

 others, &c. 



The number of transverse rows of scales is shown in 

 another column, and the average length attained by an adult 

 in the last. 



By placing all that can be expressed by simple numbers 

 in vertical columns in this way, great condensation is gained, 

 as well as facility of comparison. Expressed in words, as they 

 are at present, these numerical characters in the rat-snake (24) 

 run as follows : — There are 17 transverse rows of scales, and 

 from 190 to 208 ventrals, and 95 to 135 sub-caudals. Two 

 prae-oculars and two post-oculars ; eight upper labials, the 

 fourth and fifth entering the orbit. Two temporals immedi- 

 ately behind the orbit, succeeded by a second pair. 



It is frequently possible to determine a species of a genus 

 by means of these numerical columns only; thus, in the 

 case of the four species of Tropidonotus found in Ceylon 

 the following points can be seen at a glance by referring 

 to the table : — One prse-ocular and nine upper labials, 

 the fourth and fifth of which enter the eye, and nineteen 

 transverse series of scales serve to indentify T. asper- 

 rimus. 



T. stolatus has only eight upper labials, the third, fourth, 

 and fifth of which enter the eye. 



T. ceylonensis has two prae-oculars and eight labials, of 

 which only the fourth and fifth enter the eye. 



T % plumbicolor has also two prae-oculars, but only seven 

 upper labials. It is also at once distinguished from the 

 preceding by having twenty- three to twenty-seven transverse 

 series of scales. 



