AIDS TO THE DIFFERENTIATION OF SNAKES. 339 



quite as constant in like species as the number of rows in the middle of the 

 body. (The method of absorption, though fairly constant, does not seem to 

 me to be sufficiently so to merit special attention. In ZamerJs mucosus 

 and korros the second and third rows from the ventrals are the ones to 

 fuse usually at each step. In many Simotes the fourth and fifth become 

 blended, &c., &c.) About the region of the vent the numbers of rows 

 dwindles rapidly and inconsistently. In order to avoid conflicting results 

 I count the rows in three situations :— (1) at a spot one head's length behind 

 the head ; (2) midbody ; (3) one head's length in front of the vent. The value 

 of the results derived from points (1) and (3) is quite equal to that at point 

 (2), and, when the three are taken together, the value of the information 

 acquired is augmented threefold. 



The number is the same in all three localities in some snakes, such as 

 Bungarus, Callophis, OUgodon, Hydrophohns, Amllycephalua, Xenopeltis, &c.,&c. 

 In other snakes the number in site (1) is greater than at site (2) as in 

 Naia. Again, in other snakes the number at site (3) is less than at site (2). 

 When this occurs, it is usually less by two only, as in Psammody?iastes 

 Lycodon, &c. ; by three in one instance at least, viz., Zamenis mucosus, where 

 the original odd number 17 falls to an even one 14 ; by four rows as in many 

 Simotes, Psammoph'is condanams, Chrysopelea, &g., and by more than four in 

 Tropidonotus plumbicolor, Naia tripudians, Vipera, and many Trimeresurus. 

 In some snakes, again, the numbers are nowhere quite constant in the same 

 specimen, not even in the middle of the body as in Coluber oxycephalus and 

 many Trimeresurus, &c. It seems probable from my notes on many hundreds 

 of specimens, that these peculiarities are of generic importance and, if so 

 such closely resembling genera as OUgodon and Simotes or Hydrophohus 

 and Lycodon can be separated with ease and certainty. 



The Supra catjdals. 



In speaking of the dorsals I pointed out that the rows of scales were gener- 

 ally in odd numbers, and also made an allusion to the rapid diminution of 

 rows about the supraanal region. The rows at this site are very variable but 

 close to the base of the tail arrange themselves in eve7i numbers. As the tail 

 attenuates, these rows diminish by the absorption of two rows (one on 

 each side) at certain steps, the even numbers being retained throughout. The 

 absorption at each step is affected by a fusion of the two rows nearest the 

 median line on each side (and is different in this respect from the supra- 

 caudals of many lizards I have examined where rows nearer to the sub- 

 caudals blend). There are exceptions to this rule. In all the many Bun- 

 garus I have examined, the supracandals arrange themselves in an odd series 

 of rows to the tip of the tail, and I have also found a similar peculiarity in 

 the very few specimens of Calamaria 1 have seen. 



Another important character referable to the supracandals lies in the fact 

 that in nearly all snakes which have the vertebrals enlarged on the body 

 such as Dipsas, Dendrophis, iS:c., this peculiarity ceases in the supraanal 



