164 
OK THE PHYSIOOKOMY OF SEKPEKTS. 
Fresh-Water Serpents. These serpents approach by 
their organization more or less to the Colubri, and live in 
the water, or at least prefer the neighbourhood of rivers 
or of lakes to other places. I do not mean to say that 
all the Ophidians which have similar habitudes should be 
united to this family, otherwise it would oblige us to 
range in it the Colubri, and most of the Boas, which pre- 
sent a very different organization. I have rather as- 
sembled under this appellation the serpents of which I am 
to treat ; because, with certain analogies in their organiza- 
tion and physiognomy, they compose a natural group, but 
by no means separated by precise characters from other 
subdivisions. This family comprehends two genera, the 
first of which, with some slight exceptions, presents 
nothing interesting in the structure, while the species of 
the second are all characterized by peculiarities as marked 
as curious. The first is the 
TROPIDONOTUS, 
which constitutes an assemblage of serpents, very ana- 
logous to the genus Coluber, but the forms of which are 
more heavy ; which have the belly very broad and con- 
vex, the head broad and conical, but narro'w at the sum- 
mit, with a short muzzle. The eye is not large, and 
the nostrils are but little open. These snakes have ordi- 
narily 3 plates behind the eye ; 19 row s of scales, of a 
lozenge form, and carinated, the angle of the mouth turn- 
ing upwards. The colour of the Tropidonotus is often 
sombre, but varied with spots of vivid hues ; they do not 
arrive at a great size, and most of them do not surpass 3 
or 4 feet in length. They inhabit the vicinity of fresh- 
W'ater, or even in the water, and are very good swim- 
mers. Living in society, they are common in the places 
they frequent ; and the genus is rich in species. They 
have not yet been observed in New Holland, nor in South 
America, where they are replaced by the Homalopsis. 
Southern Africa supports but a single species, remarkable 
by its anomalous organization. 
1. Tropidonotus Natrix inhabits the whole of Europe 
