644 12. BOIDH—13. COLUBRIDZ 
County, at Hope, Bonner County, and on Fish Haven 
Creek, Bear Lake County. 
Habits.—Like the Pacific Boa, this snake has the habit 
of pretending that its very blunt tail is its head. This is 
well shown in the photograph of a living specimen (Plate 
60), where the end of the tail, held somewhat elevated and 
protected by the coils of the snake, might easily be mistaken 
for a head and perhaps save the real head from attack. 
These snakes thus merit the popular name Two-headed 
Snake. 
Family 13. COLUBRID/E 
This family contains a large number of snakes in which 
the belly is covered with a series of large plates; the head 
plates are large and more or less regular; the eye is always 
well-developed, but its pupil may be either round or ellip- 
tical; there are no rudiments of limbs or pelvis; both jaws 
are toothed, without poison-fangs near the front of the 
mouth. 
Snakes of western North America have been referred 
to 19 genera belonging to this family. These may be 
identified by the following 
Synopsis oF GENERA 
a.—Scales smooth. 
b.—Anal plate divided; urosteges in two series. 
c.—Loreal plate absent. 
d.—Anterior nasal united with internasal, sometimes 
meeting its mate on top of the snout; rostral 
prominent, greatly depressed; scales in 13 rows. 
Chilomeniscus.—p. 868. 
d’—Internasal distinct, anterior nasal not extending 
onto top of head; rostral not depressed. 
e.—Rostral not turned up at tip; scales in 15 rows. 
Tantilla—p. 875. 
