438 BULLETIN 58, UNITED STATES NATIONAL MUSEUM. 



Diagnosis. — Rostral deeper than broad; frontal small, longer than 

 broad, shorter than its distance from the end of the snout or than 

 the ])arietals; one pre- and one or two ])ostocidars; 7 or S supra- 

 labials, fourth or third and fourth entering the eye; usually a single 

 anterior temporal; [symphysial shield narrow, partly concealed in a 

 dee]) groove in the chin]; chin-shields small or indistinct; 40 to 60 

 scales round the neck, 50 to 70 round the l)ody; scales feebly imbri- 

 cate, with a small tubercle or short keel, which is stronger in the 

 males; ventrals ver}" slightly enlarged, 230-314. Young olive or 

 gray above, with black transverse bands, broadest in the middle, and 

 tapering to a point on the sides; in the adult these bands are usually 

 less distinct, some specimens being uniform dark gray above; sides 



and lower parts whitish. 



IHmensions. 



mm. 



Total length 1, 300 



Snout to vent 1, 110 



Vent to tip of tail 190 



Habitat. — The Valakadyen is introtluced here mainly on the strength 

 of a specimen recorded by Jan as being in the Milano Museum with 

 the locality "Japan." This is ordinarily a very doubtful authority, 

 and the chances are that the specimen was not taken in Japanese 

 waters. Yet, with the possibility that it may be the species which 

 von Siebold referred to in 1824 (see p. 437), I have thought it best 

 to include a brief characteristic, as it may occasionally, at least, 

 drift as far as Formosa, or farther, notwithstanding the fact that 

 it has not been reported by others north of Cochin China. 



This species is know^n from Arabia in the west to the Malay Archi- 

 pelago, Papuasia, and Siam in the east. It is said to be " incredibly 

 numerous" in the Bay of Bengal, at Pinang and Singapore. 



Genus HYDRUS" Schneider. 



1799. Hydrus Schneider, Hist. Aniph., 1, p. 2'.V6 (type, H. bicolor). 



1802. Hydrophis Latheille, Hist. Nat. Rept., IV, p. 193 (substitute for Hydrus 



Schneider). 

 ]S03. Pdamis Dauuin, Hist. Nat. Rept., VII, p. 357 (sul)stitut(> for Hydrnplns 



Latreille). 

 1830. Pelamys Wagler, Syst. Amph., p. Kili (emencUilion). 

 1848. Elaphrodytes Gistel, Naturg. Thierr., p. ix (sul)stitute f(ir Hydrus). 



The type of Hydrus, as ascertained by the process of elimination, 

 is //. platurus. I^iatreille changed the name Hydrus into Hydrophis 

 simply because the French name ".hydre" was preoccupied for 

 another animal, the Hydra. It is, therefore, a synonym pinv and 

 simple and must have the same type as Schneider's Hydrus. I)au- 

 din's Pelamis of the following year has precisely the same status, 



o From ■bSpoi, a water snake. 



