_Skull._--The skull while much shorter than that of _Sus cristatus_ from Tenasserim is actually broader. As a result the width across postorbital processes is contained only about three times in occipito-nasal length, as opposed to nearly four times in the related species. Similarly the zygomatic breadth slightly exceeds one half of the basilar length, while in _Sus cristatus_ it is less than half. Width of palate between middle molars almost exactly one sixth distance from posterior edge of palate to front of premaxillaries (measured along median line). In _Sus cristatus_ the palatal width is contained nearly seven times in the same distance. Dorsal profile of skull slightly concave near base of nasals. Zygomata heavier and deeper than in _Sus cristatus_. Audital bullæ noticeably smaller and less inflated than in the Tenasserim pig. Mandible shorter and much more robust than that of _Sus cristatus_, the outward bulge of the ramus a little behind middle of toothrow greatly accentuated. _Teeth._--As the teeth of the two specimens of _Sus natunensis_ are much worn, while those of the only skulls of _Sus cristatus_ at hand are not fully grown, it is impossible to make any accurate comparisons. The smaller size of the Natuna pig's teeth is, however, evident for the length of the entire upper toothrow does not equal that of _S. cristatus_ without the posterior molar. The crown of the middle upper molar appears to be more nearly square in outline than that of the Tenasserim pig, but in the very different condition of the specimens it would be unsafe to assume that this character is constant. _Measurements._--External measurements of type; total length 1294; head and body 1117; tail vertebræ 177; height at shoulder 558; hind foot 220 (170); ear from meatus 100; width of ear 75. Cranial measurement of type: greatest length 295 (332[10]); occipito-nasal length 282 (316); basal length 245 (275); basilar length 235 (263); length of nasals 135 (157); width of both nasals together posteriorly 34 (33); median length of bony palate 168 (183); width of bony palate at middle of second molar 30 (29); breadth between tips of postorbital processes 87 (87); least interorbital breadth 64 (65); zygomatic breadth 130 (133); occipital breadth 58 (62); occipital depth 100 (103); least depth of rostrum between canine and incisor 33 (39); mandible 225 (232); depth of mandible through coronoid process 104 (110); depth of ramus at front of first molar 40 (41); maxillary toothrow to front of canine (alveoli) 113 (131[11]); mandibular toothrow to front of canine (alveoli) 120 (138); crown of first upper molar 12 × 13 (18 × 16); crown of second upper molar 18 × 18 (22 × 16). _Weight._--Weight of type, 40 kg.; weight of adult female from Pulo Lingung, 35 kg. _Specimens examined._--Two, one from Pulo Laut, the other from Pulo Lingung.