264 ZOOLOGICAL GEOGRAPHY. [PART II. 
endeavour to ascertain the meaning of this special relation at 
a subsequent stage of our inquiries. 
Plate V.—Rwer Scene in West Africa, with Characteristic 
Animals.—Our artist has here well represented the luxuriance 
and beauty of a tropical forest; and the whole scene is 
such as might be witnessed on the banks of one of the 
rivers of equatorial West Africa. On the right we see a 
red river-hog (Potamocherus penicillatus), one of the hand- 
somest of the swine family, and highly characteristic of the 
West African sub-region. In a tree overhead is the potto 
(Perodicticus potto), one of the curious forms of lemur con- 
fined to West Africa. On the left is the remarkable Pota- 
mogale velox, first discovered by Du Chaillu,—an Insectivorous 
animal, with the form and habits of an otter. On the other 
side of the river are seen a pair of gorillas (Zroglodytes gorilla), 
the largest of the anthropoid apes. 
The bird on the wing is the Whydah finch (Vidua paradisea), 
remarkable for the enormous plumes with which the tail of the 
male bird is decorated during the breeding season. The crested 
bird overhead is one of the beautiful green touracos (Z'uracus 
macrorhynchus), belonging to the Musophagide, or plantain-eaters, 
a family wholly African, and most abundant in the western 
sub-region. 
Reptiles—In this class we find a large number of peculiar 
forms ; 13 genera of snakes, 3 of lizards, and 2 of tortoises being 
confined to the sub-region. The snakes are Pariaspis, Hlapops, 
and Prosymna (Calamariide), Rhamnophis, Herpetethiops, and 
Grayia (Colubrid), Neusterophis and Limnophis (Homalopside), 
Simocephalus and Holwrophis (Lycodontide) ; Pelophilus (Pytho- 
nid); EHlapsoidea (Elapide); and Atheris (Viperide). The 
lizards are Dalophia (Lepidosternide) ; Otosawrus (Seincide) ; 
Psilodactylus (Geckotide). The tortoises, Cinyais (Testudinide) 
and Tetrathyra (Trionichide). 
Amphibia.—Of Amphibia, there are 2 peculiar genera of tree- 
frogs, Hylambatis and Hemimantis, belonging to the Polype- 
datide. 
