COMPENDIUM OF GENERIC DISTINCTIONS. 
Genus.—Ziphius. 
upper jaw toothless, lower with two large, 
Throat furnished with two diverging 
Dorsal fin. 
Jaws tapering, 
compressed teeth. 
furrows. Lower jaw broad. 
Genus.—Ménodon. 
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.—Behiga. 
Both jaws with conical, deciduous teeth. Head rounded. 
No dorsal fin. 
Genus.—Phocena. 
Both jaws with compressed and permanent teeth. Dorsal 
fin triangular, and placed in the middle of the back. 
Genus.—Delphinus. 
Head beaked, and rather convex in front. Dorsal fin ful- 
cate in centre of back. Teeth many, small and conical. 
Sub-order._STIRE NTA. 
Body hairy. Muzzle with bristles. Two nostrils at extre- 
mity of snout. Fore-limbs like arms, hinder like fin or tail. 
Genus. —MA4natus. 
1—1 « 0—0 8—8 
=n 0a see = 34, 
Tail or caudal fin rounded and oblong. 
In adults the incisors are wanting, and in the young animal 
they are very small, 
Teeth. 
Genus.—Halicoré. 
1—1 0—0 5—5 
—I. C. M. 
0=0'  0=0’ 5—5 
Tail or caudal fin semi-lunar. Incisors are large in adults. 
Teeth. 
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. Caninesabsent. Molars very few, and separated 
by a wide intervals from the incisors. 
Feet furnished with claws. 
Family.—Mtrw 2. 
Teeth.—Lower incisors compressed and pointed. Molars 
generally six in each jaw. 
Limbs.—Fore-feet with four toes, hind-feet with five. 
Genus.—Mus. 
as ) 
Teeth.—I. : = 1 = : ,M.2 — = 16. Incisors mostly 
2— 
smooth. 
Limbs.—Fore-feet with four toes, and a nailed wart instead 
ofathumb, Hind-feet with five toes. 
Habitat.—All lands. 
789 
Genus.—Cricétus. 
Teeth.—Incisors smooth, lower compressed. Molars with 
tubercles. 
Head,—Ears rounded. 
Limbs.—Feet as in Mus. 
Tail.—Very short, and covered with hair. 
Habitat.—Northern Europe. 
Cheek-pouches. 
Genus.—Arvicola. 
Teeth.—I. = iP : = M. Dr = 16. Molars curiously 
folded so as to pas a ae series of triangles on their 
crowns. 
Head.—Ears rounded and very short. 
Limbs.—Feet as in Mus, soles without hair. 
Tail.—Rather short. 
Habitat. —Europe. 
Fenus.—My odes. 
Teeth, as in Arvicola, 
Head.—Ears not visible beyond the fur. 
Limbs.—Feet with soles hairy, fore-feet with digging 
claws. 
Tail.—Very short, covered with hair. 
Habitat.—Norway and Sweden. 
Sub-family.—Castorina. 
Teeth.—Incisors covered with coloured enamel, and smooth 
in front. Molars with four folds of enamel. 
Limbs,—Feet with five toes, hinder feet webbed. 
Head.—Ears small and round. 
venus. —Castor. 
poste! = i 0: 
n= —l —3 
Limbs.—Hind-feet nore ae 
Tail.—Wide, flat, and covered with scales. 
Habitat.—North America and part of Europe. 
Genus.—Myopotamus. 
Teeth, as in Castor. 
Limbs.—Only four toes of hind-feet webbed. 
Tail.—Round and hairy. 
Habitat.—Chili. 
Genus.—Fiber 
Se eS UES 16. 
Teeth. 79 
ae ee ae flattened. 'Toes of hinder feet 
long, and edged with thick, stiff hairs. 
Tail.—Moderate and compressed, a few short hairs appear- 
ing through the scales with which it is covered. 
Habitat.—North America. 
Genus.—H¥dromys. 
= : He il 
Teeth— vie), M. 
paler =i peal =I 
Limbs. re feet partially webbed. 
Tail.—Round, hairy, and large at the base. 
Habitat.—New Holland and Van Diemen’s Land. 
12. 
Sub-family.—Lchimina. 
Teeth.—Incisors straight, and abrupt at their extremities. 
