Summary. 1. A review of the literature on S. prasina (Newm.) is given together with its classification, systematics, and distribution. 2. The bionomics of this insect is discussed. It is pointed out that for the most part the insect inhabits turbulent mountain torrents and requires water of extreme purity and high oxygen content. Its food, size, optimum, maximum, and minimum temperatures, its respiratory movements, locomotion, and reactions to light are discussed. Its enemies and known parasites are noted. An instrument for determining spot velocities in turbulent water is described. 3. The detailed anatomy of the nymphal and imaginal instars is given and differences from the generalised insect-type indicated. Chief among these are the nymphal adaptations of the tibio-tarsal region of the legs correlated with its aquatic habitat; and the presence of a gas in the crop and gizzard of the imagines. Finally, in connexion with the venation, it is concluded that M5 is not present in Stone-flies. 4. The venation of brachypterous males is described and shown to differ but little from the general condition; it is, however, more variable. The distal branching of Rs, M, and Cu show the greatest variation, and the cross-veins are greatly reduced in number. Bibliography. Balfour-Brown, F., 1932. Textbook of Practical Entomology, Edward Arnold and Co., London. Clemens, W. A., 1917. An Ecological Study of the Mayfly, Chirotenetes, Univ. Toronto Studies, Series No. 17. Comstock, J. H., 1918. The Wings of Insects, Comstock Publishing Co., N.Y. Crampton, G. C., 1923. Phylogenetic Comparison of the Maxillae throughout the Orders of Insects, N.Y. Ent. Soc., Vol. 31, No. 2, pp. 77–106. Hudson, G. V., 1892. Manual N.Z. Entomology, West Newman and Co., London. ——, 1904. N.Z. Neuroptera, West Newman and Co., London. Hutton, F. W., 1898. “On N.Z. Neuroptera,” Trans. N.Z. Inst., Vol. 31, p. 212. Imms, A. D., 1925. Textbook Entomology, Methuen and Co. Ltd., London. ——, 1929. Some Methods of Technique Applicable to Entomology, Bull. Ent. Res., Vol. 20, Pt. 2, p. 165. Lameere, A., 1922. Bull. Clas. des Sci. Acad. Roy. Belg., Series 5, No. 8, p. 138. Martin, J. F., 1916. Thoracic and Cervical Sclerites of Insects, Annals Ent. Soc. Amer., Vol. 9, p. 35. McLachlan, R., 1865–67. New Genus of Perlidae, Trans. Ent. Soc. London, p. 354. Miall, L., and Denny. A., 1886. The Cockroach. Lovell Reed and Co., London. Newman, E., 1845. Addendum to the “Synonymy” of the Perlites, The Zoologist, Simpson Marshall Hamilton Kent and Co., London, pp. 851–53.