321 MAMMALIA. 



tuse ; muzzle beak-formed, not elongated ; number of teeth 

 middling ; without dorsal fin- 



Delphinus leucas — The Beluga. — Plate XXV. fig. 5. — 

 Head like that of the porpoise, teeth short, blunt, nine o!i 

 each side in both jaws ; instead of a fin, a small dorsal emi- 

 nence ; colour yellowish-white. From twelve to eighteen feet 

 long. Inhabits the Northern Seas. 



Sub- Genus 4. — Heterodon. — Lacepede. — One tooth in 

 each jaw, sometimes none ; lower jaw larger than the upper. 



Delphinus heterodon The Hornfleur Dolphin. — Head 



round, terminated by a round depressed beak ; no teeth ; palate 

 supplied with small points, or false teeth; lower jaw very 

 thick in proportion to the upper one ; spiracle orifice semilunar ; 

 colour gray above, and whitish below. Twenty-three feet long. 



Genus 5. — MoNODOif. — LinncEus. 



Generic Character. — Incisors, J-J, no canines nor grinders •, 

 total 2. One or two large, straight, very long and pointed tusks 

 inflated in the upper jaw ; shaped like the dolphins ; orifice of 

 spiracles united on the top of the head ; with a longitudinal 

 dorsal projection. 



Monodon vionoceros. — The Narwal. — Plate XXV. fig. i. 



Described, vol. III. p. ^76. 



Tribe II. — Large- Headed Cetacea. 



Genus 6. — Physeter.— Zinnaas. 



Generic Character. — Lower jaw elongated, narrow, corres- 

 ponding to a furrow in the upper, with from 18 to 25 thick 

 conical teeth on each side ; upper jaw broad, elevated, with 

 bony laminse, or having short and undeveloped teeth ; orifice 

 of spiracles united at the upper end of the snout ; some spe- 

 cies with a dorsal fin, others have simple eminences ; upper 

 part of the cranium having cartilaginous cavities, filled with oily 

 matter, which chrystalises when cool, forming spermaceti. 



Sub-Genus 1. — Catodon. — Lacepede. — Orifice of spiracles 

 placed at the extremity of the upper part of the muzzle ; with- 

 out dorsal fin. 



