_Heterodon d’Orbignyi_, being a small and delicate snake, was not again enticed to exhibit its jaws; but my forbearance was otherwise rewarded. One day it was dining off a rather large frog, and its mouth, close to the glass, was stretched open to its fullest extent. The frog had disappeared so far as to be within the mouth, wedging it wide open; and I then saw a fang well erected and in use, _moving_, being detached, in fact, from the food. It appeared to be somewhat nearer to the front than _Xenodon’s_ fangs, with perhaps only three or four simple teeth before it. But that it was a sheathed fang and _mobile_ I have no doubt whatever, having seen it very distinctly. I told Tyrrell at the time that _Heterodon’s_ fangs were also moveable; but now for the first time I impart this new secret to the public. _Xenodon_ also greedily seizes upon inconveniently large frogs, but it has never displayed its fangs to me while feeding, as the pretty little _Heterodon_ did. One more singular thing did this little _Heterodon_, and that was to assist itself by coiling its body round an unmanageable frog one day. It did not regularly constrict it in order to kill it; but _when caught_ in the mouth, it helped itself to restrain the straggling limbs by a few coils. Dr. Wucherer affirms that he had never seen its congeners _Liophis_ or _Xenodon_ squeeze or coil themselves round their prey, but _Heterodon d’Orbignyi_ certainly does. Another peculiarity of the American _Heterodons_ is that of flattening their heads and the upper part of the body when angry or molested. It is this, together with their pseudo-fangs, that have procured them the name of ‘spread-head,’ ‘spreading-adder’, ‘puffing-adder’ or ‘blowing viper’,—because at the same time they hiss violently,—or simply ‘the adder,’ and ‘_blausser_,’ or the blower. There are several species of them, all, with the exception of _H. d’Orbignyi_, having undeniably ugly, viperish-looking heads, ‘_Anguis capitæ viperino_,’ or ‘_Serpent à la tête de vipère_.’ The snout terminates in a large, conspicuous, recurved scale which gives them a pug-nosed or rather a hog-nosed appearance. Catesby, who was the first to describe the ‘hog-nosed snake,’ said ‘it hath a visage terrible and ugly.’ In _H. niger_ and _H. platirhinos_ this is most apparent. They belong mostly to the New World, both north and south. One in Virginia is called, from its bright markings, the ‘calico snake,’ the word calico in America being applied chiefly to coloured prints used for dresses. Another is called ‘the mountain moccasin,’ the latter name in the United States being applied to venomous kinds. In the flattening of the head and body, _Xenodon_ and _Heterodon_ approach the cobras; in the strange dentition they approach the vipers; in their true nature they are harmless colubers: thus do we see the wonderful links or gradations between opposite families, which have been such a perplexity to the early naturalist.