CROTALIDA. 85 
two sides, thus dividing the sac into an anterior and _ posterior 
part. 
A fibrous filament has one of its ends attached to the poste- 
rior extremity of the triangular sac and the anterior extremity 
attached to the base of the fang; along this filament are sus- 
pended a series of fangs, six or seven in number, the one next 
the fixed one being somewhat shorter, and the successive ones 
diminishing in size, the last being scarcely a line (one-eighth 
of an inch) in length. 
By this beautiful and curious disposition of nature, the ser- 
pent can use its teeth and mouth for mastication, without any 
particle of food coming in contact with the apparatus which 
contains and ejects the poison. If a fang is broken or falls 
off, the filament contracts and draws a spare one to its place, 
which soon becomes fixed, and the apparatus is again in 
working order. 
The color and yariegations of the skin of this species differ 
in different places, those found in North America (as pre- 
viously stated) having yellowish sides, covered with chocolate- 
colored spots, and a reddish-brown back. The varieties which 
are found in the United States of Colombia (Crot. fasciatus) 
are of a dun or seedy-black color on the back, and the whole 
length of the body divided into alternate stripes or bands, 
about three inches in width, beginning close to the head: the 
first one is of a smooth green; the next of an identical color 
with the back; the following one of the same color as the 
first band; and so on to the anus,—the last band being 
greenish and the rattle a dun color. The belly is greenish- 
white on the sides, and this shades down imperceptibly to a 
pale lead-color below. 
These South American varieties are shorter than those 
found in the temperate zones, and are always found on hill- 
sides where the surface is broken, and on stony or rocky 
