ATDS TO THE DIFFERENTIATION OF SNAKES. 343 



Coluber oxtjcephalus. — Interuasal, nasal, loreal, praeoc., frontal, 

 Hydropholus nympha. — Internasal, nasal, two pr^oc., supraoc., frontal. 

 Dendrophis. — Internasal, nasal, loreal, prseoc., supraoc., frontal. 

 Callophis Uhronii. — Internasal, nasal, 3rd laKial, eye, supraoc., frontal, 

 Naia tripudians. — Internasal, prseoc, sujDraoc, frontal. 

 Bungarus. — Internasal, nasal, prseoc., supraoc, frontal, 

 Amblyceplialus. — Internasal, prseoc,, eye, supraoc,, frontal. 

 The Frontal, 

 This scale exhibits many important differences, and its characters are so 

 well preserved in species of a like genus that, from the shape alone, with a 

 little practice, one may often make a shrew i guess at the genus a given speci- 

 men belorgs to. The number of scales with which it contracts a relationship 

 is variable, and though this may generally be worked out fiom descriptions 

 usually given in books, the due prominence this variability demands can only 

 be attained by an expression of that number. Thus it is most usually six, as 

 in Zamenis, Simotes, &c. It may be seven, as in Platuncs cokibrinus ; 

 eight, as in Lycodon auUcus,{noTi:md.\lj), Coluber oxycephalus, Simotes splendidus, 

 Zamenis arenarius, and Hipistes ; s,iid. nine, as Xenopeltis and Zamenis 

 diadema (normally). 



Certain measurements are useful guides in differentiation. Of these one 

 most usually quoted, viz., that of its length compared with its distance to 

 the end of the snout, I coi,sider of little value. I find this very variable in 

 like species of like size, and still more pronounced in young specimens com- 

 pnred with adults, and I have for this reason ceased to record it in my notes 

 The measurements I think of value are as follows :—(a) The breadth of the 

 scale compared with the total breadth of the crown between the eyes, and to 

 obtain precise results, an imaginary line is drawn across the crown connecting 

 the centres of both eyes. In Dryophis and Fsammodynastes it is about one- 

 quarter the width or less ; in Naia about one-third ; in Bungarus and 

 Callophis, about a half or more ; in Simotes and Lycodon, about three-fifths ; 

 and in Amblycephalus, Lytorliijnchus, XylopMs, Cantoria, &c., about two- 

 thirds. (6) Its greatest length compared with that of the supra-ocular is 

 useful in some cases. The three scales are usually sub-equal, but in many 

 Lycodon, and in Platurus, the frontal is one-third longer, and in Cantoria, 

 Xenopeltis, Xyloplus^ (fee,, it is twice the length of the supra-oculars. (c) The 

 relative lengths of the sutures, especially when these are six, are of great 

 importance. As a rule, the supra-oculars are the largest, as in Zamenis, Dipsas, 

 &c. Sometimes they are even twice the suture made with the parietals, as in 

 Dryophis, and some Psammophis, many Coluber, and many Tropidonotus. In 

 Cantoria, XylopMs^ &c., the supra-oculars are the smallest sutures. The 

 parietals are usually the smallest sutures, as in Chrysopelea, and Dryophis, but 

 they may be the largest as in Fordonia, and many Hydrophiince. Again, 

 sometimes the prefrontals are the largest sutures, as in some Amblycephalus. 

 sometimes the smallest sutures, a,s in many Distira, 



