Muzzle very broad, truncate, convex, swollen above. Ears without any conch. Eyes prominent. Canines very large, exserted. Cutting-teeth 4/2 in young, and 2/2 in adult; grinders all single-rooted. The anterior feet as large as the posterior ones; the fingers decrease in a curved line, destitute of claws; the hind feet with five toes, very gradually increasing towards the inner, all provided with claws; palms and soles hairy in the young, becoming chaffy. Tail rudimentary. Skull with no postorbital processes. A distinct alisphenoid canal. Mastoid process strong and salient, with its surface continuous with the auditory bulla. The scapula, hinder margin nearly straight, with the spine a short distance from and somewhat parallel with it. Resting on its body with the fore feet extended and the hind feet doubled under it, moving by the exertion of the abdominal muscles. (See P. Z. S. 1853, p. 112.) 1. TRICHECHUS. Trichechus, _Gray_, _Cat. S. & W._ p. 35. 1. Trichechus ⸺? Trichechus rosmarus, _Schrenck_, _Amur-Land_, p. 179. Inhab. North Pacific. Family 3. OTARIADÆ. Nose simple; muffle rather large, callous above and between the nostrils. Ears with a cylindrical, external conch. Arms and legs rather elongate. The fore and hind feet fringed. Fore feet fin-like, with a scolloped naked membrane. Palms and soles bald, longitudinally grooved, more or less triangular. Fingers gradually diminish in size from the inner side. Hind feet elongate, narrow, all clawless. Toes nearly of equal length, the outer one on each side being rather the strongest (see Cat. Seals and Whales, p. 44, f. 15). Three middle toes clawed. The fur is generally provided with a more or less thick under-fur. Skull with a postorbital process. An alisphenoid canal. Mastoid process strong and salient, extending aloof from the auditory bulla. Cutting-teeth 6/4, upper often bifid; canines conical; grinders 5/5 or 6/5. The scapula is curved backward to the upper angle, but with its spine or crest near the posterior margin. Testicles enclosed in the small external scrotum. They walk on their fore and hind limbs; they rest with the hind part of the body bent down, and the legs directed forward, like the Morse. The females lie on their backs to receive the caresses of the male; and the young are born on shore and are gradually taught to swim. Otariadæ, _Brookes, Mus. Cat._ 1836, pp. 18, 28; _Gray_, _Ann. & Mag. N. H._ 1869, iv. p. 268; _Gill_, _Proc. Essex Inst._ 1866, v. p. 7; _Allen_, _Bull. Mus. Comp. Zool._ ii. p. 27. Arctocephalina, _Gray_, _Cat. S. & W._ p. 44.