_Worker._ Length 1-1/2--2 lines. Shining black; the mandibles pale, ferruginous, with their inner margins finely denticulate; the eyes placed rather forwards on the sides of the head, the latter emarginate behind. Thorax deeply strangulated in the middle; the metathorax elevated and obliquely truncate behind. Abdomen ovate; the scale of the petiole sub-incrassate, with its margin rounded above; the insect very thinly covered with a fine cinereous pile. _Hab._ Aru. 13. FORMICA ANGULATA. F. nigra nitida; flagello capite antice pedibusque obscure ferrugineis, metathorace angulato. _Worker._ Length 3 lines. Shining black; head of moderate size; the clypeus and mandibles obscure ferruginous; the flagellum fusco-ferruginous, with the tip pale testaceous. Thorax rounded anteriorly and compressed behind; the scutellum prominent, forming a small tubercle; the metathorax obliquely truncate, the margin of the truncation elevated, so that when viewed sideways the metathorax forms an obtuse angular shape. Abdomen ovate, the node of the peduncle elevated, incrassate, rounded anteriorly, and flat behind. _Hab._ Aru. Gen. POLYRHACHIS, _Smith_. 1. Formica sericata, _Guer. Voy. Coq. Zool._ ii. 203; _Atlas Ins._ pl. 8. f. 2, 2 _a_, _b_, _c_, _d_, [Symbol: Mercury]. (Polyrhachis sericata, _Smith, Append. Cat. Form._ p. 200.) _Hab._ Aru; New Hebrides. 2. Formica sexspinosa, _Latr. Hist. Nat. Fourm._ p. 126, pl. iv. f. 21 [Symbol: Mercury]. (Polyrhachis sexspinosa, _Smith, Cat. Form._ p. 56. 3.) _Hab._ Aru; India; Philippine Islands. 3. POLYRHACHIS MARGINATUS. _P._ niger; antennis, palpis pedibusque ferrugineis; thoracis marginibus recurvis, metathorace petiolique squamula bidentatis. _Worker._ Length 2-1/2 lines. Black; the antennae and legs ferruginous; the head and thorax rugose; the prothorax transverse, its anterior margin slightly curved, with the lateral angles produced forwards and very acute; the thorax narrowed to the metathorax, which is armed with two divergent acute spines. Abdomen velvety black and globose; the scale of the petiole produced laterally into long, bent, acute spines, which curve backwards to the shape of the abdomen. _Hab._ Aru. 4. POLYRHACHIS HOSTILIS. _P._ niger, longitudinaliter striatus, thoracis marginibus expansis, metathorace squamulaque petioli spinis duabus crassis acutis curvatis. _Worker._ Length 3 lines. Black; the head and thorax longitudinally striated, the abdomen very finely and evenly so; the prothorax transverse, wider than the head, the anterior and lateral margins recurved, the latter acute at their anterior angles, and rounded at the posterior ones; the lateral margins of the mesothorax recurved, a deep notch between the meso- and metathorax; the latter with a long, stout, curved, acute spine on each side. The scale of the petiole produced above on each side, into a long, curved, stout, acute spine, which curves backwards round the sides of the abdomen. _Hab._ Aru.