Teeth various; sometimes entirely wanting: body fish-shaped: anterior extremities in the form of fins; posterior united, forming a flat horizontal tail.

* Grinders with flat summits: nostrils at the ex-tremity of the snout, not acting as blow-holes: whiskers very distinct: mammce pectoral.

(1). Manatus

Grinders eight or nine on each side above and below; with two transverse ridges on the summits: no incisors or tusks in the adult state: vestiges of nails on the margins of the pectoral fins.

(2). Stellerus

A single grinder on each side above and below; summit flat with projecting plates of enamel: fins without vestiges of nails.

** Teeth, when present, conical: nostrils opening on the crown of the head, acting as blow-holes: whiskers none: mammce near the anus.

† Head small: blow-holes united.

27. Delphinus

Both jaws with numerous teeth, all simple and equal.

(1. Delphinus). Snout produced into a beak, broad at its base, rounded at its extremity, and separated from the forehead by a kind of furrow: a dorsal fin.

(2. Phoccena). Snout short and blunt; not beaked : a dorsal fin.

(3. Delphinaptera). Head blunt; snout not produced: no dorsal fin.

28. Monodon

Head blunt: no true teeth; upper jaw with one, rarely two, very long straight tusks projecting forwards in a line with the body: no dorsal fin.

29. Hyperoodon

Snout produced: teeth generally but two in number, placed in front of the lower jaw: palate studded with tubercles: a dorsal fin.

††Head very large; half or one third of the entire length.

30. Physeter

Head enormously large, truncated in front: upper jaw without whalebone or visible teeth; teeth in the lower jaw numerous: blow-holes united.

(1. Catodon). No dorsal fin.

(2. Physeter). An elevated dorsal fin.

31. Balaena

Head very large: palate furnished with whalebone: no teeth : blow-holes separate.

(I. BalAEna). No dorsal fin.

(2. BalAEnoptera). A dorsal fin.