Abstract
Tillyard, in his “Insects of Australia and New Zealand,” (1926) figures (p. 264) a sawfly, Xiphydria decepta Smith, in which the vein separating the first and second marginal cells in called rm2 (second radio-median cross-vein); it is the r of MacGillivray (1906). On page 290 he figures an ant ( Polyrhachis ammon Fabricius), the base of the marginal cell being duly labelled rm2. A more primitive ant ( Myrmecia gulosa Fabricius), on page 287, shows the same thing. There can be no doubt that this vein forms the base of the marginal cell as understood in most of the higher Hymenoptera. The base of the first marginal cell in sawflies is the radial sector according to MacGillivray, but Tillyard regards it as rm1 (first radio-median cross-vein). This is the vein which becomes obsolescent or disappears, as shown by Miss Gibbons. However, as MacGillivray shows (Proc. U. S. Nat. Museum, XXIX, 1906), in numerous genera of sawflies it is the rm2 (or his r) which has disappeared, while rm1 (or Rs) remains. In this regard it is interesting to consider the Mesozoic and Eocene family Pseudosiricidae. Tillyard (Trans. Ent. Soc. London, 1927) actually refers the British Eocene form ( Megapterites mirabilis Cockerell) to Siricidae. In former times, the Mesozoic representatives were thought to be ants, or allied thereto, and Westwood named one of them Formicium brodiei (for a figure, see Canadian Entomologist, January, 1921, p. 22). But the wing-structure is closely similar to that of the Siricidae, and is not like that of the ants. More recently (Journal Washington Academy of Sciences, 19, August, 1929) Carpenter has described a large form from the Lower Eocene of Tennessee, regarding it as an ant, and naming it Eoponera berryi . Comparison of his figure (p. 301) with the wing of Megapterites (Canad. Ent., Jan., 1921, p. 22) shows that it is nearly the same, but rm2 has disappeared. The base of the marginal cell is rm1, as may be seen in sawflies, but apparently never in ants.
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