354 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



Fossil remains of Cheiroptera, although of rare occurrence, are 

 found as far back as the upper Eocene, from the deposits of which 

 period a limited number of forms, representing in the main modern 

 genera, have been described. The oldest known forms are Ves- 

 perugo Parisiensis, much resembling the broadly distributed sero- 

 tine, from the gypsum of Montmartre, Vespertilio Morloti from the 

 nearly equivalent deposits of Switzerland, and Vesperugo velox, 

 V. priscus, and Nyctilestes serotinus from the United States. In 

 this family of placental mammals alone do representatives of exist- 

 ing genera extend to such an ancient epoch as the Eocene. A 

 species of Rhinolophus, R. antiquus, has been described from the 

 phosphorites of Quercy, France usually referred to the Oligocene 

 period while a generically related form, Palseonycteris, occurs in 

 the Miocene. The Miocene deposits of both France and Germany 

 also contain several species of the genus Vespertilio. Post-Pliocene 

 or late Pliocene cave-remains closely approximate the forms now 

 living in the equivalent or adjoining region. The early specialisa- 

 tion of this class of animals, concerning whose differentiation prac- 

 tically nothing is known, indicates a most ancient line of ancestry, 

 which must be traced far into the Mesozoic era. 



Ho dent ia. With the exception of the bats the rodents are the 

 only order of terrestrial mammals which can be said to have a 

 nearly universal distribution, being found in all the primary zoo- 

 geographical regions but the Polynesian. On the continent of 

 Australia, however, only a single family, that of the mice (Muridae), 

 is represented, and that by a comparatively limited number of spe- 

 cies ; the squirrels have a few representatives in the Austro-Malay- 

 sian transition-tract. 



Of the four great divisions into which the rodents are divided, 

 the myomorphs, or mouse-forms, are numerically much the most 

 important, the family of mice alone comprising considerably more 

 than one-third of the total number of species some eight hundred 

 or more belonging to the order. The geographical distribution 

 of this family is practically coextensive with that of the order. 

 The mice proper (Mus), of which there are upwards of one hundred 

 species known, are restricted exclusively to the Old World, over 

 which they are very extensively distributed ; they are almost wholly 

 wanting in the Pacific and the greater number of the Austro-Malay- 

 sian islands, but are found sparingly in both Australia and New 



