This is a very singular insect in many respects, and closely resembles in form the _Formica truncata_ of Spinola. 9. FORMICA QUADRICEPS. _F._ nigra, nitida; capite antice oblique truncato, thorace postice compresso. _Worker._ Length 3-1/2 lines. Shining black; head oblong-quadrate, slightly narrowed anteriorly, with the sides nearly straight, the posterior angles rounded, and very slightly emarginate behind; the head obliquely truncate from the base of the clypeus; the truncation as well as the mandibles obscurely ferruginous; the apex of the flagellum and the apical joints of the tarsi pale rufo-testaceous. Thorax rounded anteriorly, compressed behind, with the metathorax abruptly truncate. The scale of the petiole narrow, incrassate, its anterior margin slightly curved, its posterior margin straight; the abdomen ovate. _Worker minor._ About 3 lines long, very like the larger _worker_, the head being truncate in front; but it is, in proportion to the thorax, narrower; the latter is compressed and abruptly truncate; in other respects it agrees with the _worker major_. _Hab._ Aru. 10. FORMICA LAEVISSIMA. _F._ nigra nitida laevissima, sparse pilosa; squama oblonga subdepressa. _Worker._ Length 4 lines. Jet-black, very smooth and shining; head wider than the thorax, slightly emarginate behind, the sides slightly rounded; the anterior margin of the clypeus rounded, the mandibles striated and obscurely ferruginous; the scape with a few glittering silvery-white hairs. Thorax not quite so wide as the head anteriorly, narrowed behind, with the disk somewhat flattened, slightly convex, a deep strangulation between the meso- and metathorax, the latter obliquely rounded; the legs and abdomen sprinkled with glittering white hairs. The node of the petiole incrassate, very slightly elevated; viewed sideways, broadly wedge-shaped; the abdomen ovate. _Hab._ Aru. 11. FORMICA NITIDA. _F._ capite abdomineque nigris, antennis thoraceque pedibusque rufo-testaceis laevissimis et lucidis. _Worker._ Length 4 lines. Head and abdomen shining black; the flagellum, thorax, legs, and scale of the petiole rufo-testaceous; the legs palest; the scape fuscous, with its base pale; the head large, wider than the abdomen, and emarginate behind; the clypeus and mandibles obscurely ferruginous. Thorax compressed, not strangulated in the middle. The scale of the petiole narrow, with its margin rounded above; abdomen ovate, and sprinkled with a few erect pale hairs. _Hab._ Aru. 12. FORMICA SCRUTATOR. F. nigerrima, mandibulis tarsorumque articulo apicali pallide ferrugineis, thorace medio profunde coarctato.