434 



MANUAL OF ZOOLOGY. 



six feet in length, and the neck can be extensively dilated, 

 covering the head like a hood. A nearly-allied species is the 

 Naia Haje (fig. 167) of Egypt. Also in this section are the 

 venomous Water-snakes {Hydrophidce), which have a com- 

 pressed tail, and are adapted for an aquatic life. They mostly 

 frequent the mouths of rivers in droves, and they swim with 

 great grace and rapidity. 



A very good general character by which the Colubrine snakes 

 may be distinguished from the Viperine snakes, is in the shape 

 and armature of the head. In the Viperina, as before said, 

 the head (figs. 166, 168) is triangular, broadest behind, and 

 separated from the neck by a more or less marked diminution 

 in the diameter of this latter part. The scales, too, which 

 cover the head are of small size. In the Colubrine snakes, on 

 the other hand, the head is not markedly triangular, and gra- 

 dually tapers off into the neck, whilst the upper surface, of the 



Fig- 1^8.— A, Head of Colubrine Snake (Colnler aatrix) ; B, Head of Viperine Sna 

 (feims berus); C, Head of Wmi-voTmi^Auguis fragilis), one of the serpentiform 

 Lizards. (After Bell.) 



head is usually covered with large shield-like plates or " scuta" 

 (fig. 168, A). 



Distribution of Ophidia in Time. — The Ophidiaaxe: not 

 known to occur in any Paleozoic or Mesozoic deposit. The 

 earliest-known traces of any serpent are in the Lower Kaino 

 zoic Rocks, the oldest being the Palaophis toliapicus of the 

 London Clay of Sheppey. The nearly-allied Palaophis typhxus 

 of the Eocene beds of Bracklesham appears to have been a 

 Boa-constrictor-like snake of about twenty feet in length, 

 f ther species oiPalczophis\isst been described from the Tertiary 



