Haemaphysalis (Kaiseriana) mageshimaensis sp. n., a member of the H. (K.) bispinosa group, is described from males, females, nymphs, and larvae from pasture vegetation (and laboratoryreared) from Mage Island in Kagoshima Prefecture, Japan. The sika deer, which is common on Mage Island, appears to be the original host. Most of the cattle on the island are infected by Theileria sp., which is probably transmitted by this tick. In the laboratory, the life cycle is completed in 93 to 108 days. Normal bisexual reproduction, with 1,000 to 1,500 eggs per female, almost 100 per cent larval hatching, and approximately equal numbers of F1-F3 males and females, was observed, as well as an appreciable though limited degree of true parthenogenetic reproduction, with few eggs, low larval hatching rate, absence of mating, and only female F1 adults. No males of this species mated with bisexual or parthenogenetic females of H. (K.) longicornis Neumann. Male longicornis mated with female mageshimaensis, but four or five days after mating almost all sperm had disappeared from female organs, the larval hatching rate was low, and all progeny consisted of mageshimaensis females. Haemaphysalis (K.) mageshimaensis sp. n., from a Japanese island with a subtropical or temperate climate in the eastern part of the Palearctic Faunal Region, is a member of the H. (K.) bispinosa group (Saito and Hoogstraal, 1972) which originated in tropical forests of the Oriental Faunal Region. This new species is noteworthy in that it may reproduce either bisexually or parthenogenetically. A related species, H. (K.) longicornis Neumann of Japan and nearby areas of continental Asia (Hoogstraal et al., 1968), reproduces chiefly parthenogenetically in the northern area of its range and chiefly bisexually in the southern area. Interbreeding between parthenogenetic and bisexual populations of H. (K.) longicornis is unknown. Received for pubpication 19 January 1973. *From Research Project MF33.0524.009-3010B, Bureau of Medicine and Surgery, Department of the Navy, Washington, D. C. The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the Department of the Navy or of the naval service at large. The illustrations in this report were prepared under the auspices of Agreement 03-005-1 between the NIAID (NIH) and NAMRU-3. t Medical Zoology Department, Niigata University School of Medicine, Niigata City, Japan. t Medical Zoology Department, U. S. Naval Medical Research Unit Number Three (NAMRU-3), U. S. Interests Section, c/o Spanish Embassy, Cairo, Arab Republic of Egypt. Parthenogenesis does not appear to occur in other Haemaphysalis species and may be an adaptation to the cool climate inhabited by these two members of a group that otherwise exists only in a tropical environment. Haemaphysalis (Kaiseriana) mageshimaensis sp. n. Mage Island haemaphysalid