Eylais warkawae n.sp. (Hydracarina) and Some Features of Its Life History and Anatomy By Vida M. Stout, Zoology Department. Victoria University College [Read before Wellington Branch, February 3. 1953: received by Editor, February 6, 1953.] Abstract Eylais warkawae is described and found to be closely related to the previously described New Zealand species, Eylais schauinslandii. The principal differences include the absence of a pan of bristles on the eye-bridge; the absence of coarse Innition with scattered giaining on the skin of the body; the angled not rounded anterior point of the mandible; the more slender P. III with no projection from the distal flexor surface; the outer row of five, not nine, short spines on P.IV, and the presence of three pairs of genital plates in the female. A general account of development in the Hydracarina is included and the life history of E. wraikawae described and shown to agree with the general pattern. Details of the life history such as the method by which the larva hatches, its attachment to the host and the emergence of the nymph and adult are described. An account of the anatomy of the female of Eylais waikawae is given and agrees with that given by Croneberg for E. extendens in 1878 except in the shape and structure of the mouth glands, the more extensive branching of the excretory system and the presence of a median unpaired nerve innevating the pharynx. The internal organs have undergone modification from the normal acarid plan, especially in the development of a large sac-like ventrieulus and extensive branchings of the exeretory and reproductive systems. Introduction and Technique The Hydracarina have been neglected in New Zealand, where only one species. Eylais schauinslandii Koenike 1900, has been so far described. This was collected at D'Urville Island by Professor Schauinsland during a voyage in 1896 and 1897. The species is listed by Hutton (1904) and by Lamb (1952). White (1900) refers to minute arachnids travelling rapidly over the surface of the water, but not entering the water. These probably belonged to the Genus Notaspis, a member of a terrestrial family but often found on the surface of the water or on water plants. Two species of the closely related marine mites, Halacaridae, have been described by Chilton (1883) from Lyttelton Harbour. In Australia the Hydracarina are a little known group. The major work is by Lundblad (1947) who describes species sent to him by H. Womersley. Lundblad's paper includes nearly all the Hydracarina described from Australia previously to 1941, but does not mention the three species described by Rainbow (1905–1907), Eylais maccullochi Rainbow, Hydrachna odontognathus Canest., and Atax cumberlandensis Rainbow. Hydracarina are probably widespread in New Zealand, although the number of species may not be large. In this work for the study of the external morphology both canada balsam and Diaphane gave satisfactory mounting media. For anatomical studies Schaudinn's fixative, with three to four additional drops of acetic acid, was used, the chitin being softened by immersion in chlorinated