SYNOPSES AND DESCRIPTIONS. 109 



PLATYCERCA. 

 HYDROPHIDAE. 



Sea serpents. Venomous. Elongate, subcylindrical anteriorly, com- 

 pressed posteriorly ; head rather indistinct, generally depressed ; tail short, 

 compressed into a paddle. Eye small, pupil round. Fang small, erect, 

 grooved in front, followed by other teeth. Nostril valvular. Head-shields 

 generally irregular. No loreal. Scales small, with or without keels, or 

 tubercular. No claw at the side of the vent. Hab. tropical portions of 

 the Indian and Pacific oceans, sometimes entering fresh waters. 



Pelamys. 



Daudin, 1803. 



Moderately long; neck rather large; head depressed; snout long, broad. 

 No internasals. Nasals in contact, nostrils near the hinder margins. No 

 loreal. Scales small, not imbricate. Ventrals indistinct or small. Lower 

 jaw not notched in front. One species of this genus is frequently met with 

 off the western coasts of Southern Mexico. 



Pelamys platura. 



Much compressed posteriorly; neck stout; head little larger than the 

 neck, long, depressed; snout long, broad, and rounded in front; tail short, 

 of moderate width. Head-shields abnormal. No internasals. Nasals 

 longer than broad, nostril near the outer posterior angle. Prefrontals 

 hexagonal, receiving the anterior angle of the frontal between them. No 

 loreal. One anteorbital, sometimes two. Two to three postorbitals. 

 Labials 7 — 9, second larger. Scales polygonal, commonly hexangular, 

 not imbricate ; lower with a convexity or tubercular keel ; upper flat. 

 In the specimen before me there are 53 rows around the middle of the 

 body. Ventral scales similar. 



Back (23 rows of scales) and top of head black. Upper lip and lower 

 half of body yellow. Lower lip marked with black. Tail with three 

 transverse bands of black, the rounded ends of which extend near the 

 lower margin, where they alternate with four spots of black. Vent in a 

 spot of black. Tip of tail black. The coloration varies greatly in differ- 

 ent individuals. The specimen described was taken on the western coast 

 of Nicaragua. 



