524 PHILOSOPHICAL TRANSACTIONS. [aNNO 178^. 



the venomous colubri, the proportion is still less. In the atropos it is found 

 only-rV* I" ^^^ English viper, coluber berus, it is commonly about 4- or -i-. In 

 some venomous species however the proportion is something greater. In the 

 naja it is sometimes -^ ; which proportion is, he thinks, as great as he has ever 

 observed : at any rate he never met with a venomous serpent the tail of which 

 was equal to -i- of the whole length. With respect to those colubri which are 

 not venomous, there are many whose tails are within the limits assigned to the 

 venomous ones. In the coluber ^sculapii, doliatus, getulus, and some others, 

 the tail is not generally more than -f of the whole length. In the lemniscatus it 

 sometimes does not exceed -j^ or -j-V? t>ut perhaps in no other Linnaean species 

 it is so short. In the greater number however the proportion of tail is more 

 considerable ; in many it is full ^. In the ahaetulla, and in some species not 

 described by Linnaeus, it is sometimes more than ^ ; but never quite so long as 

 the trunk, or half of the whole length. None of the Linnaean species, of the 

 Boae, have their tails either remarkably long, or short ; but in 2 species, not 

 described by Linnaeus, Dr. G. has found the tail very little exceeding the pro- 

 portion here assigned to the coluber lemniscatus. In the thickness of the tail, 

 or in the acuteness of its termination, he has observed no difference worth re- 

 marking. In every species of the first 3 genera, the tail is thinner than the 

 trunk ; and in most of them it is more or less acute. The few exceptions he 

 has observed were none of them venomous ; but they are too few to deserve any 

 particular consideration. 



A character of great use in distinguishing the species of serpents, and which 

 was not overlooked by Linnaeus, is that elevated line, or carina, v/ith which the 

 scales of many species are furnished. In order to show how far this is to be 

 considered as serving to distinguish venomous serpents from others. Dr. G. has 

 examined 112 species of serpents, not venomous, belonging to the first 3 

 genera ; and found that 80 of them have smooth scales, and 32 only have cari- 

 nated ones. Of venomous serpents he has examined 26 ; of which number, 20 

 have carinated scales, and only 6 have smooth ones. On the whole therefore, 

 carinated scales must be considered as being, in some measure, a character of 

 venomous serpents. 



The other 3 genera, anguis, amphisbaena, and caecilia, besides the characters 

 assigned them by Linnaeus, have some others which are common to all, and 

 which render them very different, in their external appearance, from any of the 

 first 3 genera. These are, a very thick and obtuse tail, and a head which is 

 very indistinct, and furnished with very small eyes. This last character is some- 

 times, though very rarely, met with among the colubri, for instance, in the 

 lemniscatus ; in the last 3 genera however it takes place without exception. 

 The thickness of the tail is also common to every species ; and though in the 



