788 



COMPENDIUM OF GENERIC DISTINCTIONS. 



Genus. Didelphys. 



Teeth. I. 



55 



C. 



i i 



P. 



33 



M. 



44 



50. 



44 i i 33 44 

 Two middle incisors of upper jaw rather longer than 

 others, and separated from them by a slight interval 

 Upper canines stronger than the lower Prae- 

 molars conical Molars furnished with sharp cusps. 



Head. Long, gape of jaw very far back. 



Pouch. Tolerably developed. 



Tail. Long, covered with fur at the base, and 

 with scales towards the extremity ; prehensile. 



Genus. Cheironectes. 



Feet. Toes of the hinder-feet connected by a 

 web. There is also a development of the pisiform 

 bone, which supports a fold of the skin, and looks 

 like a sixth toe. 



Pouch. Well developed. 



Tail. Longer than body. 



Family. 



Teeth. Incisors variously deciduous ; molars with 

 flattened crowns, or sometimes furnished with cusps. 



Feet. Furnished with five toes, short, and pal- 

 mate ; the hinder-feet being turned backwards so as 

 to approach each other. 



Body. Gradually tapering from the shoulders to 

 the tail, which is very short and conical. Clothed 

 with smooth hair, pressed firmly against the body. 



Sub-family. Phocina. 



55 66 

 Teeth. Incisors permanent ; molars - , or - . 



5-5 55 

 Ears. Very small, or wanting. 



Genus. Leptonyx. 

 22 i i 33 

 Teeth. I. - , C. - , P. - , M. 



22 i i 33 

 Incisors much pointed; molars divided into three 

 long, conical, and slightly curved points. 

 Head. Muzzle narrow and elongated. 

 Neck. Long and tapering. 

 Limbs. Nails very small, especially those of the 

 hinder-feet. 



22 



22 



32. 



Genus. Stemmatopus. 



Teeth. I. 



2 2 



C. 



I I 



p. 



33 



2 2 



M. = 30. 



I I I I 31 22 



Incisors conical ; canines stout and large. 



Head. Adult male furnished with a large mem- 

 branous and muscular sac, which is divided into two 

 channels by a development of the septum of the 

 nose. 



Genus. Phoca. 



Teeth. I. 



33 



C. 



P. 



33 



2 2 



M. = 34. 



2 2 



I I 33 . . 



All the molars except the first furnished with double 

 roots. 



Genus. Trichecus. 



1 eeth. Upper canines enormously developed, and 

 without roots. 



Head. Muzzle tumid and protuberant, covered 

 with thick bristles External ears wanting. 



Genus. Morunga. 

 Teeth as in Stemmdtopus. 

 Head. Proboscis-like expansion of nose. 



Genus. Arctocephalus. 



22 



I I 



22 



or 



rarely 



2 2\ 



2 2/ 



34. 



33 

 Four upper and middle inci- 



sors broad crowned, with groove, two others coni- 

 cal. 



Limbs. First toe of fore-feet longes't, the middle 

 hinder-toes nearly equal ; membrane of hinder-feet 

 projecting like leathern straps beyond the toes. 



Order. CETE. 



Teeth. When present, conical and similar, the 

 palate frequently furnished with baleen. 



Body shaped like a fish. 



Limbs. Short and fin-shaped, the hinder pair 

 forming a horizontal tail. 



Skin. Smooth and hairless, nostrils developed 

 into blowing-tubes. 



Family. 



Nostrils two, palate with baleen, jaws without 

 teeth. 



Head. Very large, equal to one-third the size of 

 the body. 



Genus. Balaena. 



No dorsal fin, abdomen smooth, baleen very long. 

 Teeth. None in adult, only rudimentary in young. 



Genus. Megaptera. 



Dorsal fin, abdomen furnished with longitudinal 

 folds, pectoral fins long, equalling the head in length, 

 baleen short, broad, and triangular. 



Genus. Balaenoptera. 



Dorsal fin sharp and falcate, abdomen and throat 

 furnished with longitudinal folds, pectoral fins mod- 

 erate, baleen short. 



Genus. Physalus. 



Dorsal fins falcate, pectorals moderate, abdomen 

 and throat with longitudinal folds. Blow-holes 

 semi-lunar, divided from each other by a groove, 

 and covered with a valve or flap. Baleen short. 



Family. CATC^NTID.*. 



Head very large, upper jaw apparently toothless, 

 the lower jaw furnished with many conical teeth, 

 which are received into cavities in the upper jaw. 

 Blow-holes united, with a semi-lunar opening. 



Genus. Cdtodon. 



Dorsal hump rounded, blow-holes in front of the 

 head. 

 Head. Blunt at muzzle, skull much elongated. 



Genus. Physeter. 



Upper jaw longest, blow-holes on the top of the 

 head near the middle, separate, but covered with a 

 common flap or valve. Dorsal fin high and fal- 

 cate. 



Family. DELPHINID^E. 



Head moderate Both jaws furnished with teeth, 

 which are frequently shed at an early age. Blow- 

 holes united, forming a transverse semi-lunar open- 

 ing on the top of the head. 



