600 ZOOLOGY SECT. 



Neotropical regions, and the Vampire Bats occur exclusively in the 

 latter. 



The distribution of the Lemurs is remarkable ; they occur only 

 in Madagascar, a limited part of South Africa, Southern India and 

 Ceylon, some of the islands of the Malay Archipelago, and the 

 Philippines. The headquarters of the group is the island of 

 Madagascar, of -which they constitute one half of the entire 

 Mammalian fauna. 



Of the other groups of Primates, the Marmosets (Hapalidse) and 

 the Gebidai are exclusively American ; the Gercopithecidse Palse- 

 arctic. Oriental and Ethiopian, with a .single species in Mada- 

 gascar. Of the Simiidse the Gibbons occur only in South-Eastern 

 Asia and the Malay Peninsula ; the Orangs only in Borneo and 

 Sumatra ; the Gorilla and Chimpanzee in certain parts of Western 

 Equatorial Africa. 



G-eological Distribution. — The earliest fossil-remains of 

 Mammals have been found in strata of Upper Triassic and of 

 Jurassic age in Europe and America. These remains consist 

 almost exclusively of jaws and teeth, and, as the latter differ 

 widely from those of existing Mammals, there is frequently great 

 difficulty, in the absence of remains of the other hard parts, 

 in determining the affinities of these Mesozoic forms. Some 

 of the Triassic and Jurassic Mammalian molar teeth are con- 

 structed on the most primitive form of the triconodont type, which 

 has already been referred to (p. 561) as being the primitive 

 form ia the class, having three cones or cusps in a longitudinal 

 row. In Dromatherium and its allies each . molar has a single 

 main cusp with two smaller accessory cusps. There is no decisive 

 evidence as to the affinities of these primitive triconodont Mam- 

 mals, but they may be provisionally set down as allied to the 

 Prototheria. 



Of the remainder of the Mesozoic Mammals some were probably 

 Prototheria, others Metatheria, while others again may have been 

 Insectivores. Most of them fall into two main groups. The type 

 of dentition presented by the members of one of these groups 

 (Fig. 1227) is more nearly allied to that of the Polyprotodont 

 Marsupials (p. 478) than to any other. In the other group (Multi- 

 tuberculafa) (Fig. 1228) there is a superficial resemblance to the 

 Diprotodont Marsupials ; a single chisel-shaped incisor is present on 

 each side of the lower jaw, and one large, and sometimes one or 

 two smaller, on each side of the upper. A wide diastema separates 

 these from the pre-molars. The molars present a number of 

 variously-arranged small tubercles. In some cases the pre-molars 

 have a pattern similar to that exhibited by the molars, but in 

 others. they have a cutting edge which may be serrated or obliquely 

 grooved. The fact that the vestigial molar teeth of OrnitJiO' 



