Hitherto the pit has certainly plagued not only zoologists, but all classifiers of the Ophidia; because serpents that have this facial depression embrace so many widely differing genera, some of them resembling in all other respects the true vipers, and others the rattlesnakes, so that they have come to be distinguished as the ‘pit vipers.’
One of our most able biologists, A. R. Wallace, in his Geographical Distribution of Animals,[106] informs us that ‘the Crotalidæ, including the deadly rattlesnakes, abound most in the oriental regions’ (though not a single rattlesnake is found there, or in the Old World at all). Let us seek for the reason of this apparent incongruity, and how it is that a large number of serpents which have no rattle come to be placed among those which have an instrument specially constructed to produce a rattling sound.
Not to weary the reader by attempting to describe the various systems of classification adopted by the many herpetologists who were the contemporaries and immediate successors of Linnæus, we will rather invite his imagination to picture the geographical history of our globe during that age. Travels, explorations, the establishment of new colonies, and the settlement of new territories marked the era; and, as a sequence, new and hitherto unknown fauna were continually brought home to Europe. We have seen, too, how natural history had been growing into a science, and how travellers and zoologists stimulated each other by their researches and writings. To recall a few of the names with whom reptiles are associated, and to remind the reader that one arranged them according to their scales, another their form, a fourth their teeth, a fifth their habits, and so on, and that even at the present day the classification of them is far from complete, the present writer will be absolved from attempting anything beyond generalization.
Studying snakes towards the end of the last century, were Laurenti, Buffon, Bonnat, Lacepède, Klein, Seba, etc.
In the early part of the present century were Latreille, Shaw, Daudin, Oppel, Merrem, Wagler, Neuwied, Cuvier, and many others till we come to Gray, Fitzinger, and Dumeril, 1844. This last author, in his introduction to Les serpents solenoglyphes, dit Thanatophides, including the most deadly snakes, devotes several pages to the subject of the ‘pit,’ and why it had especially occupied the attention of those herpetologists who were endeavouring to improve the previously imperfect systems. Wagler in 1824 assigned the name Bothrops (from βὀθρος, any hole, or pit, or hollow dug) to vipers with the pit that had only scales and no plates or shields on their head, separating these from the rattlesnakes and from those that have shields (see illus. p. 318). This nomenclature of Wagler’s did not commend itself to other herpetologists, and Fitzinger, in his Systema Reptilium, 1843, extending the group, retained the name for one of the five families into which he divided all the venomous snakes. Fitzinger’s fifth family, the Bothrophides, included some of the Indian pit vipers; but as some of these latter have shields on their head, they could not be admitted into Wagler’s group with scales only. As the present object is to demonstrate some of the perplexities of naturalists, and to arrive at the reason why so many snakes without the crotalon are called Crotalidæ, we will quote Dumeril’s reasons, inviting the reader to picture to himself the interest with which new examples were brought home for investigation, and the obstacles presenting themselves to herpetologists, who find one feature claiming alliance to this snake, while another feature points an alliance to an entirely opposite one.
So Dumeril shows us why some of the herpetologists wished to admit every species that has the nasal fosse under the generic name Bothrophidæ, and others would have limited the term to a few, because the name does not suit them all equally well. ‘Beaucoup d’autres serpents presentent aussi des enfoncements creusés sur la tête et sur le bord des lèvres.’ These depressions, called by Professor Owen ‘secreting follicles,’ may be easily distinguished on the upper lip of some of the larger constrictors. In the Reticulated python you can count these pits like deep dimples round the mouth. In the Diamond snake (Morelia spilotes) they are remarkably deep along the lower lip.
Of those ‘follicles’ in the Crotalidæ Dumeril writes: ‘Les fossettes paraissent devoir être des organes particuliers dont l’usage ou la fonction n’est pas connu il est vraix, mais qui semble avoir quelque importance par leur position constante entre les orifices réels des narines et les yeux, at leur structure anatomique assez compliquée. À cause de la grande analogie qu’ils ont tous avec les serpents à sonnettes, nous avons preféré appeler ceux-ci les crotaliens.’[107]
The above words are under the head of ‘Les Crotaliens,’ a name retained, he had already explained why. ‘Les solenoglyphes qui ont les narines doubles en apparence seront pour nous les Crotaliens quoique cette dénomination puisse, à tort, porter à croire que ces espèces font du bruit avec leur queue: elle indique seulement leur rapports avec les crotales établis d’après la présence des fausses narines ou fossettes dont nous venons de parler. On nomme quelquefois ces Ophidiens Bothrops.’[108] ... ‘Comme ce caractère conviendrait à tous les Crotaliens parcequ’ils ont tous des fossettes dites lacrymales, ce nom (Bothrops) deviant par conséquent trop général.’[109]
In retaining Bothrops as a generic distinction, a large number of non-venomous and constricting serpents must have been included, which probably induced Wagler’s opposers to say of him that he ‘created a system in which the venomous and non-venomous were huddled together pell mell.’
Thus we see that on account of the nasal fosse the Indian crotaline snakes could not be true vipers; they could not be exclusively Bothrophidæ, for the reasons given above, and they certainly are not rattlesnakes; but for want of a better name they are ‘Crotalidæ,’ as they have (minus the rattle) more features in common with rattlesnakes than with any others.