672 CLASS XVII. 



solitary in Europe and the North of Asia, and in society now only in some 

 districts of North America. These social beavers fell large trunks of trees 

 by means of their sharp teeth for constructing domed habitations in water, 

 which they surround with a mound of trunks of trees, branches, earth, &c.^ 

 These animals are hunted for their fur and for the castoreum. This last is 

 found in both sexes in two sacs, which in the male open into a canal 

 formed in and by the prepuce, in the female into the vagina. Below these 

 two sacs lie a pair of smaller sacs, of a more elongate form, which contain 

 an unctuous matter. Compare A. C. Bonn Anatome Castoris, L. B. 1806, 

 4to, c. tab. and especially Brandt tt. Ratzeburg Medizin. Zoologie, i. s. 

 12 — 30, Tab. III. IV. where a succinct account may be found of all that is 

 known of the economy and the anatomy of the beaver from works of the 

 best authors. Brandt has recently distinguished the American beaver 

 {Castor americanus) from Castor fiber chiefly by osteological characters of 

 the skull. See his Beitrdge zur ndheren Kenntniss der Gattung Castor, 

 Mem. de VAcad. de St.-Petersbourg, vii. 1855, pp. 43 — 76. 



Myopotamus Commerson. Fifth toe of hind feet situated 



beyond the membrane conjoining the rest of the toes. Tail round, 



elongate, pilose. (Four teats on each side, nearer the back than 



the belly, covered by hair. Dental formula as in Castor.) 



Sp. Myopotanuis coypus Cuv., Myopotamus bonariensis Comm., Geopfe, 

 Saint-Hilaire Ann. du Mus. vi. PI. 35, pp. 8r, 86 — 88 ; Guer. Iconogr., 

 Mammif. .PL 29, fig. 3 ; three feet long, of which the tail forms nearly 

 one-third ; Hves in Chili in holes on the banks of rivers. Compare Lere- 

 BOULLET Notes pour servir d V Anatomic du Coipou, avec 1 pi.; Mem. de la 

 Soc. d'Hist. nat. de Strasbourg, Tome iii. 1846. The skins, which are used 

 for making hats, bear in the trade the name of ^ mertcaji Otter, and are 

 annually brought to Europe by hundreds of thousands. 



Family XXVI. Murina. Inferior incisors compressed, acumi- 



3 — 3 



nate. Molars uniformly covered by enamel, mostly — -- . Fore 



feet almost always furnished with four wide-spread toes, and a 

 wart for a thumb often unguiculate ; hind feet pentadactylous. 

 Tail most frequently long, thinly haired. Clavicles distinct. 



Compare on this family and on other genera formed from the genus 

 Mus L., A. Brants het geslacht der muizen, Berljn, 1827, 8vo. 



Hydromys Geoffr. (excl. of Hydr. coypus). Incisors smooth 



2 — 2 . . 

 in front ; molars , uniformly enamelled, crown with transverse 



ij — ^ 



^ A beaver even in solitude built in the Jardin des Plantes at Paris a wall of bark, 

 &c. to protect itself from the cold; Geoffr. Saint-Hilaibe Mem. du Mils. xii. 

 p. 232. 



