82 OPHIDIANS. 
36 rows of rhomboidal scales of a nearly uniform shape and size ; dorsal 
seales slightly oval, lanceolated ; caudal scales rhomboidal, but smaller. 
The belly is covered with from 180 to 212 consecutive half rings or - 
semi-elliptical scales (scuta) extending from the throat to the anus. Body 
thick, of a conical shape (in section), diminishing in size from its centre 
to the tail, and slightly reduced in diameter at the neck. 
The caudal extremity is provided with a series of inter- 
sected hollow rings or capsules, so arranged that they have 
great freedom of motion and flexibility (these rings are com- 
posed of a substance similar in nature to horn); a new one of 
which is added every year, so that the number of composing 
rings of the rattle (cascabel) indicates the snake’s age. 
I have seen individuals with from 5 to 21 capsules, and 
others are found at times which have from 25 to 40, and that 
individuals of this genus do attain an age of more than forty 
years seems to be a fact established beyond all reasonable 
doubt. 
The lower teeth are disposed in two concentric semi- 
ellipses (maxillary and lingual series); the upper ones in two 
series (maxillary and palatal); when the mouth is closed 
those in the lower series lie between those of the upper series 
in the spaces just outside and just inside them; all the teeth 
are curved backwards, longer or shorter according to the size 
of the individual, but of nearly an equal length. From each 
side of the upper jaw, and just back of a vertical line with the 
eye, there is a triangular-shaped bone to which the fang is 
attached ; this is curved backwards, and when erect its chord 
forms nearly a right angle with the roof of the mouth or axial 
line of the upper jaw. 
On the posterior side of its base is an articulation by which 
it is attached to the forward end of the external pterygoid 
bone ; this articulation is a fixed point upon which the fang 
hinges, its erection and depression being effected by the cor- 
