A MONOGRAPH OF THE SKA-SNAKES (HYDROPHIIN2). 249 
Fig. 64.—Hydrus platurus. 
I have examined 47 specimens besides those in the British Museum. I find the 
posterior maxillary teeth grooved. 
Description.—Rostral,—the visible portion above one quarter to one half 
the internasal suture. Prefrontals,—touch the second supralabial (rarely the 
third also). Frontal,—sutures subequal, or the fronto-supraocular rather the longest. 
Postoculars,—one or two. Temporals,—absent, replaced by small scales. 
Supralabials,—seven to ten very irregular, the third and succeeding shields very fre- 
quently divided, two sometimes three touch the eye, viz., the third, fourth or fifth. 
Infralabials,—five or six, the last in contact with three or four scales behind. 
Marginals,—none. Sublinguals,—small, an anterior pair usually more or less 
distinct, but widely separated, a posterior pair still less distinct if recognisable at all 
as such. Costals,—anterior 40 to 54, midbody 45 to 62, posterior 41 to 52 juxta- 
posed everywhere. Ventrals,—370 to 440, small but rather larger than the last 
costal row, very irregular, many being divided. 
Colour.—Vary variable. I quote from Boulenger’s Catalogue (1896). 
** 4.—Yellow, with brown, black edged cross-bands ; black bars between the cross- 
bands on the sides of the belly (P. ornata, Gray). 
B.—Anterior third of body with a black dorsal stripe ; further back, a series of 
transverse dorsal rhombs on the back, and black spots on the sides and belly. (Var. 
maculata, Jan). 
C.—Dorsal region black ; sidesand belly yellow, with a lateral series of black spots, 
which may be partly confluent 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 and belly yellow ; tail spotted as in the preceding (H. hi- 
color, Schn.). 
F.—Yellow, witha black vertebral stripe, broken up into spots posteriorly ; no 
lateral spots on the body or tail. 
G.—Yellow, with a vertebral band and spots on the tail pale brown or olive.”’ 
Habitat.—The tropical area of the Pacific Ocean, and connected waters. In Asia 
the litoral from the Persian Gulf to Yezo (N. Japan). In Africa the East Coast 
1 A modified form of this without the yellow lateral stripe occurs. One such is No. 153 in the Colombo Museum. 
