464 ZOOLOGY. 



believe these animals always for that purpose resort to holes in the sides of 

 ponds, sluggish streams, or dykes." 



The arvicoline Muridoe were present in the tertiary fliuna. Several 

 species of Arvicola or Ilypucl.nis are mentioned and described from conti- 

 nental Europe. 



The genus Stcnofiher^ referred to the arvicolines by some and to beavers 

 by others, has been established upon a skull found in the middle tertiary 

 beds of Auvergne. Its forms are intermediate between the beaver and the 

 musk-rat. • 



Suh-fam. 4. SiMlacina, of which there are no representatives in North 

 America, is a small group composed of but thirteen species, distributed into 

 seven genera, as follows: JRhizoniys, six species, Asiatic and African; 

 Tachyorydes and Heterocephalus^ each one species, both African ; Ellohius^ 

 two species, European and Asiatic ; Ommatostergus and Spalax, each one 

 species, both in France ; and Siphneus^ one species, in Siberia. 



The genus Spalax (the rat-moles) has very short legs, each foot provided 

 ■with five toes and as many flat and slender nails. The tail is very short 

 or completely wanting, and the same observation applies to the external 

 ear. They live under ground like the moles, raising up the earth like them, 

 although provided with much inferior means for dividing it ; but they subsist 

 on roots only. The blind rat-mole {S. typhius) is a very singular animal, 

 which, from its large head, angular on the sides, its short legs, and total 

 absence of a tail and of any appendage externally, has the most shapeless 

 physiognomy. In the opinion of some writers, this should be the animaj 

 alluded to by the ancients, when they spoke of the mole as being perfectly 

 blind. 



Suh-fam. 5. Ilurina, has a greater number of representatives in the old 

 than in the new world. The genera into which they are distributed amount 

 to not less than twenty-eight to thirty, and the species to more than two 

 hundred. There are comparatively very few in North America, where the 

 genera 3fu^, with eight species ; Neotoma, with two ; and Sigiaodon and 

 Hespei-omys^i with only one, in all twelve species, represent Murina. 



The Asiatic and African mice and rats are distributed into the genera 

 Isomijs, Akomys, Golunda, Vandeleuria, Nesokia, Dendromys, Pithecheir, 

 Oncetomys, Phloeomys, Psammomys, Malacothrix, Euryotis, Mystromys. The 

 genera Hapalotis and Hydromys are Australian. In South America we find 

 forty -five species of Hesperomys^ the genera Oxymyderus, Calomys, Akodon, 

 Drymomys, and Beilhrodo7i, with a few only. The European species belong 

 to the genera SmintJius, Gerhillus^ and Cricetus, which have also representa- 

 tives in Asia and northern Africa. 



The genus Mus (rats and mice) is distributed throughout the whole sur- 

 face of the globe. It is characterized by three molars on each side above 

 and below, the anterior of which is the largest ; its crown is divided into 

 blunt tubercles, which, by being worn, give it the shape of a disk, sloped in 

 various directions ; the tail is long and scaly. The ears oblong or round, 

 nearly naked. The common mouse, Mas musculus {pi. 113, fig. 8), 

 originally from the East, has been introduced into America with the white 

 668 



