COMPENDIUM OF GENERIC DISTINCTIONS. 



789 



Genus. Ziphius. 



Jaws tapering, upper jaw toothless, lower with 

 two large, compressed teeth. Throat furnished 

 with two diverging furrows. Lower jaw broad. 

 Dorsal fin. 



Genus. M6nodon. 



Few and early deciduous teeth in both jaws. 

 Forehead convex. Upper jaw of male with one or 

 two long, projecting teeth, spirally twisted. Dorsal 

 fin. 



Genus. Beluga. 



Both jaws with conical, deciduous teeth. Head 

 rounded. No dorsal fin. 



Genus. Phocaena. 



Both jaws with compressed and permanent teeth. 

 Dorsal fin triangular, and placed in the middle of 

 the back. 



Genus. Delphfnus. 



Head beaked, and rather convex in front. Dorsal 

 fin fulcate in centre of back, Teeth many, small, 

 and conical. 



Sub-order. SIRENIA. 



Body hairy. Muzzle with bristles. Two nostrils 

 at extremity of snout. Fore-limbs like arms, hinder 

 like fin or tail. 



Genus. Mdnatus. 



i i 



Teeth. I. 



C. 



o o 



88 



M. = 34. 



88 



o o o o 

 Tail or caudal fin rounded and oblong. 

 In adults the incisors are wanting, and in the 

 young animal they are very small. 



Genus. Half core. 



ncisors are large 



i i o o 5 5 



Teeth. I. , C. , M. . 



o o o o 5- 

 Tail or caudal fin semi-lunar, 

 in adults. 



Genus. Rhytina. 



Teeth none, the jaws being furnished in their 

 stead with a horny plate. Tail semi-lunar. 



Order. RODENTIA. 



Teeth. Two long, curved, sharp-edged, rootless 

 incisors in each jaw. Canines absent. Molars very 

 few, and separated by a wide interval from the inci- 

 sors. 



Feet furnished with claws. 



Family. MuRlD.*. 



Teeth. Lower incisors compressed and pointed. 

 Molars generally six in each jaw. 



Limbs. Fore-feet with four toes, hind-feet with 

 five. 



Genus. Mus. 



i i i i 2 2 



Teeth. I. , P. , M. = 1 6. Incisors 



i i i i 2 2 

 mostly smooth. 



Limbs. Fore-feet with four toes, and a nailed 

 wart instead of a thumb. Hind-feet with five toes. 

 Habitat. All lands. 



Genus. Crice*tus. 



Teeth. Incisors smooth, lower compressed. Mo 

 lars with tubercles. 



Head. Ears rounded. Cheek-pouches. 

 Limbs. Feet as in Mus. 

 Tail. Verv short, and covered with hair. 

 Habitat. Northern Europe. 



Genus. Arvfcola. 



Teeth. I. 



i I 



P. 



i i 



2 2 



M. 



= 1 6. Molars 



I I I I 2 2 



curiously folded so as to form a double series of tri- 

 angles on their crowns. 



Head. Ears rounded and very short. 



Limbs. Feet as in Mus, soles without hair. 



Tail. Rather short. 



Habitat. Europe. 



Genus. My6des. 



Teeth as in Arvicola. 

 Head. Ears not visible beyond the fur. 

 Limbs. Feet with soles hairy, fore-feet with dig- 

 ging claws. 



Tail. Very short, covered with hair. 

 Habitat. Norway and Sweden. 



Sub-family. Castorina. 



Teeth. Incisors covered with colored enamel, and 

 smooth in front. Molars with four folds of enameL 

 Limbs. Feet with five toes, hinder feet webbed. 

 Head. Ears small and round. 



Genus. Castor. 



i i i i 33 

 Teeth. I. , P. , M. = 20. 



i i i i 33 

 Limbs. Hind-feet entirely webbed. 

 Tail. Wide, flat, and covered with scales. 

 Habitat. North America and part of Europe. 



Genus. Myopdtamus. 



Teeth as in Castor. 



Limbs. Only four toes of hind-feet webbed. 



Tail. Round and hairy. 



Habitat. Chili. 



Genus. Fiber. 



I I i i 22 

 Teeth. I. , P. , M. = 16. 



I I I I 2 2 



Limbs. Claws curved and flattened. Toes of 

 hinder feet long, and edged with thick, stiff hairs. 



Tail. Moderate and compressed, a few short 

 hairs appearing through the scales with which it is 

 covered 



Habitat. North America. 



Genus. Hy"dromys. 



i i i i I i 

 Teeth. L , P. , M. 



12. 



Limbs. Hinder-feet partially webbed. 

 Tail. Round, hairy, and large at the base. 

 Habitat. New Holland and Van Diemen's Land 



Sub-family. Echimyna. 



Teeth. Incisors straight, and abrupt at their ex- 

 tremities. 



