24 BRITISH SERPENTS. 
plates on either side of these large ones. Notice that 
the eyes are opposite the row of three plates, and that 
the largest of all are the two immediately behind 
Vie. 5.—Heap PLATES 
or Rina SNAKE. 
(N, nasal; F, frontal; 8, 
supra-ocular; Py parietal.) 
these. This is different from 
the arrangement in the adder, 
but cannot be said to be a very 
ready imeans of distinguishing 
the species until it has been 
captured. The scales on the 
back are keeled or carinated— 
that is, they are possessed of a 
mid-rib like a leaf. Hence the 
generic term of “Tropidonotus,” 
which means literally “ keel- 
backed.” This keel is still more 
prominent in the adder. The 
seales along the ventral surface 
are in a single row as far as 
the anal orifice, when the row 
becomes a double one. The tail 
is about one-fourth the length of 
the whole reptile. 
The teeth are in two rows on both the upper and 
lower jaws, and are recurved, pointing to the throat, so 
that it is difficult to extract anything from the mouth 
when the jaws have closed upon it. “ They are not in 
sockets, and consequently are not used to tear or 
erush food.” ! 
1 Packard, 
