VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 525 



anguis bipes, and in another species, not described by Linnaeus, but figured in 

 Browne's History of Jamaica (Tab. 44, fig. ],) the tail has an acute termination, 

 yet in both these species, especially in the last, it continues thick, to the end, 

 and becomes suddenly sharp, being what in botanical language would be called, 

 obtusa cum acumine. With respect to the proportionate length of tail however, 

 it is very remarkable that the genus anguis affords examples of much less pro- 

 portion, and also of much greater, than is to be found in any of the first 3 

 genera. In the anguis scytale the tail is not above -^ of the whole length ; in 

 the maculata it is not above Vir ; y^t in the anguis fragilis, and in the ventralis, 

 the tail is always longer than the trunk, or is more than half the whole length. 

 Indeed, in one specimen of the last-mentioned species. Dr. G. found the tail 

 nearly |- of the whole length. It may however be questioned whether that 

 species is really an anguis, or a lacerta. 



The principal inferences to be deduced from those remarks, are the following: 

 1st. That a broad head, covered with small scales, though it be not a certain 

 criterion of venomous serpents, is, with some few exceptions, a general character 

 of them. 2dly, That a tail under -i- of the whole length is also a general cha- 

 racter of venomous serpents ; but since many of those which are not venomous 

 have tails as short, little dependance can be placed on that circumstance alone. 

 On the other hand, a tail exceeding that proportion is a pretty certain mark that 

 the species, to which it belongs, is not venomous. 3dly. That a thin and acute 

 tail is by no means to be considered as peculiar to venomous serpents ; though a 

 thick and obtuse one is only to be found among those which are not venomous. 

 4thly. That carinated scales are, in some measure, characteristic of venomous 

 serpents, since in them they are more common than smooth ones, in the pro- 

 portion of nearly 4 to 1 ; whereas smooth scales are, in those serpents which 

 are not venomous, more common, in the proportion of nearly 3 to 1. 



On the whole therefore it appears, that though a pretty certain conjecture may, 

 in many instances, be made from the external characters; yet, in order to de- 

 termine with certainty whether a serpent be venomous or not, it becomes ne- 

 cessary to have recourse to some more certain diagnostic. This can only be 

 sought for in the mouth. To those who form their ideas of the fangs of veno- 

 mous serpents from those of the rattle-snake, or even from those of the English 

 viper, it will appear strange that there should be any difficulty in distinguishing 

 those wea{)ons from common teeth; and indeed the distinction would really be 

 very easy were all venomous serpents furnished with fangs as large as those of 

 the fore-mentioned species. But the fact is, that in many species the fangs are 

 full as small as common teeth, and consequently cannot, by their size, be known 

 from them; this is the case with the coluber kticaudatus, lacteus, and se- 

 veral others. 



