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1. These studies were originally intended to form the basis of a world monograph of the Siricidae ; such a work cannot be completed under present circumstances.2. Two ratios are introduced as useful characters for separating species : the ovipositor/forewing ratio and the sawsheath/ovipositor ratio. These ratios were obtained from all specimens of all the species represented in the British Museum collections and the results are tabulated. They were found not to vary with the size of the insects.The former ratio is specially useful in the genus Urocerus, which has a long ovipositor, and the latter ratio in the genus Sirex, which has a shorter ovipositor.3. Keys are given to the genera of the world. Of Semenov's new genera, Xoanon is accepted but not Xanthosirex. A new genus Eriotremex is erected for certain Indo-Malayan species previously included in Tremex.4. Keys are given to the European species, which are compared critically with related species from other parts of the world. A key to the species of Eriotremex, gen. nov., is also given.5. Sirex noctilio, F., and S. juvencus, L., are recorded for the first time from North America and S. cyaneus, F., from the continent of Europe. The common Urocerus of the northern Palaearctic region is shown to be more closely related to the Nearctic U. gigas flavicornis, F., than to the central European U. gigas gigas, L., and is treated as a new subspecies—U. gigas taiganus, subsp. nov. U. gigas tibetanus, subsp. nov., is described from the Himalayas. U. sah, Mocsáry, is treated as a subspecies of U. augur, Klug, and U. cedrorum, Smith, as a synonym of U. augur augur, Klug.6. The British Siricidae are discussed, and it is suggested that U. gigas taiganus, subsp. nov., and the form of S. juvencus, L., with entirely black antennae may be native in the Caledonian forest.7. It is argued that modern Siricidae could not have been derived from the Jurassic Pseudosiricidae.8. The known Oriental and Himalayan Siricidae are listed and discussed. Urocerus multifasciatus, Takeuchi, and Eriotremex formosanus, Matsumura, are mentioned as two species originally described from Formosa but shown also to occur on the mainland. Urocerus niger, sp. nov., is described from the Himalayan region, and the name Eriotremex malayanus, sp. nov., is given to a form described without a name by Forsius from Malaya.9. Several errors in previous work on Siricidae are corrected.

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The Macrotermitinae are a large and successful subfamily of fungus-growing termites, characterised by their symbiotic association with white-rot fungi of the genus Termitomyces. The taxonomy of the subfamily, and in particular of the largest genus Odontotermes, is problematic. We used sequences of the mitochondrial 16S gene from termites occurring in East Africa and Malawi to explore the phyletic relationships within the genus Odontotermes and to place the genus in the broader context of other fungus-growing termites. We also interpret this phylogeny in relation to classical morphological taxonomy in the form of absolute and relative dry weights of the sterile castes, and in relation to innate behaviour as shown by nest architecture and fungus comb structure. This work lays the foundations of a complete taxonomic revision of the Macrotermitinae.The phylogeny supports one clear subdivision, here called the "tanganicus" group, within the genus Odontotermes. It also supports the significance of field observations on the structure of fungus combs, as the whole "tanganicus" group builds fungus combs of the sponge type (or modified forms thereof) which are hardly known elsewhere. Other phyletic relationships are less clear, the residual sequences being referred to as the "latericius" group. We recognise three probable miniature species within the "tanganicus" group and another possible one in the residual "latericius group".