HYDROSAURUS. 195 



rivers and lakes, leading a subaquatic life. It is a generally received 

 opinion, that they keep pretty much on the surface of the ground, 

 seldom, if ever, venturing to climb on trees or rocks. In the journal 

 kept on board the squadron by the naturalists of the Expedition, we 

 find the following observation on the habits of an Australian species, 

 which will be read with interest : " This large reptile (three to four feet 

 in length), appears to be by no means rare. One seen at Pewen Bewen, 

 by Mr, Dana and myself, immediately mounted a tree rather leisurely 

 and with measured pace, and ascended to one of the topmost branches, 

 where it fixed itself, without regarding any further attempt to dislodge 

 it, and, indeed, from the height and scarcity of suitable missiles, it was 

 more secure than would appear at first. This, we were informed, is its 

 usual custom." [Pickering.] 



Syn. — Varanidae, Bonap. Saggio, Distr. Anim. Vertebr. 1831. 

 Varmiiens, DuM. & BiBR. Erpet. gen. Ill, 1836, 437.— DuM. & A. Bum. Catal. 

 meth. Kept. Mus. d'hist. nat. 1851, 49. 



Monitoridae, GaAY, Ann. Nat. Hist. I, 1838 j & Catal. Lizz. Brit. Mus. 1845, 6. 



Most of the living representatives of this family inhabit the Old 

 World, with the exception of the heloderms, which are Americans. 

 Many species, some of huge dimensions, have left their remains in the 

 solid strata of the globe in both hemispheres. 



Genus HYDROSAURUS, Wagl. 



Gen. ChAe. — Body covered with small scales. Head elongated, sub- 

 pyramidal. Teeth compressed, sharp-edged, denticulated. Nostrils 

 oblong, longitudinal, near the apex of the muzzle. Tail very long, 

 provided above with a double-edged keel. Toes unequal, elongated, 

 and compressed. 



^Y^.—Hydrosaurus, Wagl. Naturl. Syst. Amph. 1830, 164.— Gray, Catal. Lizz. 

 Brit. Mus. 1845, 6 & 12. 



Obseev. — Wagler was led into error as to the disposition of the 

 dorsal scales, which are placed side by side, surrounded with small 

 granules, instead of being imbricated and deprived of these same 



