46. HYDRUS 893 
tals. Nostrils open upward in large nasal plates. No inter- 
nasals. Lorea] present or absent. Ocular plates variable. 
Seven to 11 supralabials. Anterior genials sometimes present. 
Scales on body smooth, hexagonal, juxtaposed, in from 45 
to 61 rows. No large gastrosteges or urosteges. Tail short, 
high and thin, paddle-shaped. In males the scales have 
central tubercles. 
The color above is dark brown or bluish black on about 
15 or 17 rows of scales, changing abruptly, along a more or 
less straight line, to the light yellow, brownish yellow, or 
yellowish brown of the sides and lower surfaces. The tail 
is light yellow with dark blotches. 
Jkengthe to) anise eS ee 
Length of tail 
Distribution—This snake occurs nearly everywhere 
along the coasts and islands of the Indian and warmer por- 
tions of the Pacific oceans. It has been found in the Hawaiian 
and Galapagos islands and is common along the coast of 
Central America. 
Mocquard records two specimens captured in the Gulf 
of California near Espiritu Santo Island. 
Cope mentions it from “Pacific coast Guaymas?” 
Habits—This is a marine species, and probably eats 
fish. 
Family 16. CROTALIDAE 
The Crotalide or Pit Vipers are represented in western 
North America by fifteen kinds of rattlesnakes. These are 
our only poisonous serpents, except the little coral snake 
(Elaps or Micrurus), and may be distinguished from the 
harmless forms by their possession of a pit in the side of the 
face between the eye and the nostril, and a horny, segment- 
