Tetramorium electrum, Bolton, B., 1979

Bolton, B., 1979, The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Malagasy region and in the New World., Bulletin of the British Museum (Natural History) Entomology 38, pp. 129-181 : 144

Tetramorium electrum sp. n.

(Fig. 20)

Holotype worker. TL 4.9, HL 1.14, HW 1.06, CI 93, SL 0.82, SI 77, PW 0.76, AL 1.32.

Mandibles longitudinally striate but only shallowly so, the sculpture reduced in some paratypes. Clypeal margin with a median notch or impression. Frontal carinae long and strong, reaching back almost to the occipital corners and surmounted by a narrow raised rim or flange. Antennal scrobes shallow but broad, the scrobal area above the eye traversed by about four widely spaced longitudinal rugulae, the space for accommodation of the scape unsculptured. Maximum diameter of eye about 0.20. Pronotal dorsum in dorsolateral view feebly transversely concave, the remainder of the dorsum more or less flat transversely and marginate laterally so that sides and dorsum meet in a sharp angle. Propodeal spines very long, in profile downcurved along their length. Metapleural lobes reduced to low, rounded vestiges (Fig. 20), not at all triangular and scarcely prominent in profile. Petiole with a long peduncle and relatively high node (Fig. 20), in dorsal view very slightly longer than broad. Dorsum of head with spaced-out longitudinal rugulae, many of which are discontinuous and which do not form a reticulum occipitally. Spaces between rugulae with slight, very faint ground-sculpture, extensively shining. Dorsal alitrunk centrally with a series of parallel, strong longitudinal rugae which run from anterior pronotum to propodeum. Outside of these are a few disorganized longitudinal rugae and close to the margins there is a tendency for a rugoreticulum to form. Dorsal surfaces of both petiole and postpetiole with faint traces of weak rugulation, which is stronger on the sides; gaster unsculptured. All dorsal surfaces of head and body with numerous fine, acute hairs. Colour dark brown.

Paratype workers. TL 4.7 - 5.2, HL 1.04 - 1.20, HW 0.96 - 1.16, CI 92 - 96, SL 0.74 - 0.86, SI 72 - 78, PW 0.72 - 0.82, AL 1.24 - 1.40 (11 measured). Maximum diameter of eye c. 0.20 (about 0.17 - 0.19 x HW). As holotype but some specimens darker in colour, blackish brown, and a few with the mandibular sculpture reduced and quite faint.

Holotype worker, Madagascar: Rte d'Anosibe, km 33, 4 - 12. iv. 1975 forest humus and litter, AB 44 (A. Peyrieras) (MCZ, Cambridge).

Paratypes. Madagascar: 11 workers with same data as holotype (MCZ, Cambridge; BMNH); one worker, vic. Andasibe (= Perinet) 950 - 980 m, 2 - 6. ii. 1977 {W. L. & D. E. Brown) (MCZ, Cambridge).

The exceptionally long, downcurved propodeal spines, reduced metapleural lobes and large size will differentiate electrum from all members of its group. The only other species of the group in which the metapleural lobes are reduced is kelleri , but here they are still prominent and the node is very differently constructed (compare Figs 13 and 20).