158 THE SNAKES OF SOUTH AFRICA. 



up on shore, there are some which make frequent inland excur- 

 sions, sometimes to considerable distances over the land, usually 

 at night, when the vegetation is moist. Sea Snakes are most 

 abundant in the Tropical portions of the Indian Ocean and 

 Western Pacific. Some species congregate in great shoals, and 

 swarm in the cracks and crannies of ocean rocks which are sub- 

 merged at high tide. If poked with a stick they bite viciously, 

 after the manner of venomous land snakes. 



Sub-family HYDROPHIN^E. 



The various Genera and Species of Sea Snakes belong to the above sub-family . 

 They are all very venomous, possessing grooved fangs at the anterior end 

 of the upper jaw. 



Genus HYDRUS. 

 This Genus is represented by only one Species. 



KEY TO THE SPECIES. 



Rostral as deep as broad or a little broader than deep ; frontal large, 

 at least as long as the snout or the parictals, one or two pre- and 

 two or three postoculars ; one or two suboculars sometimes present ; 

 temporals small and numerous ; seven or eight upper labials, second 

 in contact with the prefrontal, fourth, fifth ; or fourth and fifth 

 usually entering the eye ; chin shields small and indistinct ; 45 to 

 47 scales round the body, smooth in the female and young ; laterals 

 and ventrals rough, with one, two, or three small tubercles in the 

 male. 

 I. Hydrus platurus. Black and Yellow Sea Snake. 



Synonyms — A nguis platurus ; Hydrus bicolor ; Pelamus bicolor ; Pela- 



mus platurus. 

 Colour — Markings very variable. 



A. Yellow, with brown, black-edged cross bands ; black bars between 



the cross bands, on the sides of the belly. 



B. Anterior third of the body with a black dorsal stripe ; further 



back a series of transverse dorsal rhombs on the baclv, and black 

 spots on the sides and belly. 



C. Dorsal region black ; sides and belly yellow, with a lateral series 



of black spots which may be partly continent into a stripe ; tail 

 with dorsal and lateral spots. 



D. Dorsal region black, ventral region brown, the two separated by 



a yellow lateral stripe ; tail spotted as in the preceding. 



E. Black above ; sides of belly yellow ; the two colours do not 



blend. There is a distinct line of demarcation. Tail spotted 

 as in the preceding. 



F. Y''ellow, with a black vertebral stripe, broken up into spots poste- 



riorly ; no lateral spots on the body or tail. 



G. Yellow, with a vertebral band and spots on the tail pale brown 



or olive. 

 Average length — 2 feet. 

 Distribution — Coast of South Africa ; Indian Ocean and Tropical 



Pacific. 



