VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 523 



seum Regis, and in the introduction to the class amphibia, in the Systema 

 Naturae, it seems that he thought it not easy to distinguish them by any exter- 

 nal characters ; and his ideas respecting the venomous fangs themselves were so 

 vague and confused, that it was hardly possible for him to attempt to found a 

 generic distinction on them. 



Whether venomous serpents can be with certainty distinguished from others, 

 and if so, how they are to be known, is what is meant to be considered in this 

 paper ; in doing which Dr. G. examines, first, how far they may be distinguished 

 by any external characters ; 2dly, supposing the venomous fangs to be the only 

 certain criterion, how those fangs are to be distinguished from common teeth. 

 Though serpents, by their internal organization, , naturally belong to the 3d 

 class of the animal kingdom, they are in their external form more simple than 

 most of the animals belonging to the 3 inferior classes ; their external charac- 

 ters must consequently be very few. 



In the 1 St genus, crotalus, the head is broader than the neck, depressed or 

 flat at top, and covered with small scales. These 3 characters are particularly 

 observable in the 3 intermediate species horridus, dryinas, and durissus. In the 

 miliarius the scales of the head are rather larger than in the others. The mutus 

 certainly sheuld not be placed among the crotali. As all the species of this 

 genus are venomous, one is naturally led, by the examination of it, to consider 

 the fore-mentioned characters as being, in some measure, proper to venomous 

 serpents. In the genus coluber are many venomous species, and it is very cer- 

 tain that in general they have the fore- mentioned characters ; examples of which 

 may be seen in the atropos, cerastes, atrox, berus, and others. It is however 

 equally certain that there are some in which they are not to be found. For 

 example the naja, a species well known to be very venomous ; the head of which 

 is neither depressed nor broad, is covered with large scales, and is in every 

 respect a complete exception to what has been said respecting the heads of 

 venomous serpents. Since then there are venomous serpents in which the fore- 

 mentioned characters, viz. a broad and depressed head, covered with small scales, 

 are not to be found ; let us examine whether those characters are to be found in 

 any of those serpents which are not venomous. In the genus coluber there are 

 very few, except venomous ones, which have the head much broader than the 

 neck ; and of those few every one has the head covered with large scales. But 

 in the genus boa, though no species is venomous, except the contortrix, almost 

 every one has the head broad, depressed, and covered with small scales. The 

 canina, constrictor, hortulana, besides some others not described by Linnaeus, 

 furnish examples of this. 



In the crotali Dr. G. has never found the tail, exclusive of the rattle, to 

 exceed j^ part of the whole length ; sometimes it is much shorter. In some of 



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