40 REPTILES. 
**k*** Head small; frontal shields 2, transverse, band-like ; rostral 
triangular, subangular. 
37. PRosyMNa. 
D. Head covered with small scales: tail with one row of shields be- 
neath ; abdominal shield broad, rounded, smooth: nostril in a 
shield, anterior, sublateral : scales granular, with rows of keeled 
scales. Xenodermina. 
38. XENODERMUS. 
I. Tail compressed, except in Acrochordus. Belly keeled, with two 
rows of small scale-like shields, often united together into a single, 
broad, six-sided, often two-keeled shield. The anterior teeth large, 
and grooved on the front edge. Venomous. 
Hydrina, Gray, Zool. Misc. 59, 1842. _ Hydride, Gray, Ann. 
Phil. x. 1825, 206. Colubroidea, § 1, and Bungaroidea, § 1, Fitz. 
N. Syst. Rept. 32, 1826. Hemiophidia, fam. Nectopus, and Cha- 
linophidia, fam. Hydrophis, Fitz. Consp. Ophid. 1846. Hydrus, 
Schneid. H. Amph. i. 233. Latr. Rept. iv. 293. Daud. Rept. vii. 
372. Cuv. R. A. ii. 74, ed. 2, 11.97. Merrem, Tent. 138. Hydro- 
phis, Oppell, Rept. 59, 1811. Pelamis, Daud. Rept. vii. 357. 
These are true sea-snakes: they coil themselves up on the shore, 
living on sea-weeds, and lay their eggs on the shore: they are often 
found asleep on the surface of the sea, when they are easily caught, 
as they cannot descend without first throwing themselves on their 
back, probably to repel the air in their large vesicular lungs, (see 
Grey's West. Australia, 445). Often thrown ashore by the surf: 
they are sometimes found in rivers, having been brought in by the 
tide, but they can live only a short time out of salt water. They 
are often caught in nets, and are held in great dread by the fisher- 
men, on account of their venomous bite. 
The pupil is round: Lesson (Voy. Belanger) erroneously repre- 
sents it as linear and erect. 
The separation of the specimens of this family into species and 
genera is attended with great difficulty; the form and number of 
the shields of the head, lips, temple and chin, are liable to great 
variation, not only in the different specimens, but often in the two 
sides of the same individual. The two ventral series of scales are, 
in the same specimen, sometimes separate, and at other times united 
