PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 116(4):943-955. 2003. A new genus and new species of the family Paguridae (Crustacea: Decapoda: Anomura), from Hachijo-jima Island, Japan, with a list of hermit crab species found in the same collection sites Masayuki Osawa and Junji Okuno (MO) Department of Zoology, National Science Museum, Tokyo, 3-23-1, Hyakunincho, Shinjuku-ku, Tokyo 169-0073, Japan, email: osawam@kahaku.go.jp; (JO) Coastal Branch of Natural History Museum and Institute, Chiba, 123, Yoshio, Katsuura, Chiba 299-5242, Japan, email: okuno@chiba-muse.or.jp Abstract.—A new genus and new species of pagurid hermit crab, Hachijo- pagurus rubrimaculatus, is described and illustrated on the basis of three spec- imens from Hachijo-jima Island in the Izu Islands, Japan. The new genus Hach- ijopagurus appears close to Pygmaeopagurus McLaughlin, 1986, but differs from the latter in having the eighth thoracic sternite with a pair of ventrally flattened lobes in male and female, and a rod-like sexual tube on the coxa of the right fifth pereopod in male. The distinct concavity at the dorsomesial distal angle of the palm of the right cheliped can be regarded as unique for H. rubrimaculatus since such the structure has not been described for any known pagurid species. A list of the hermit crab species found in the collection sites of the present new species is provided. Kato & Okuno (2001) introduced the richness of the shallow-water decapod crus- tacean fauna around Hachijo-jima Island of the Izu Islands, Japan, in their local guide- book "Shrimps and crabs of Hachijo Is- land", with many underwater photographs. Their book contains a photograph of an un- usual hermit crab, "Paguridae sp.", taken at the depth of 40 m. The photographed specimen could be collected, and was found to have a characteristic right cheliped with a distinct concavity at the dorsomesial distal angle of the palm. In addition to this spec- imen, two hermit crabs proved to be con- specific with Kato & Okuno's (2001) "Pa- guridae sp." from Hachijo-jima Island were made available for close taxonomic study. The examination of the three specimens re- vealed that they represent an undescribed species that can not be assigned to any known pagurid genera. Thus, we herein de- scribe and illustrate these specimens as a new genus and new species. General terminology used in the descrip- tion follows that of McLaughlin (1974:9), with the exception of the posterior carapace (see Lemaitre 1995:2), fourth pereopod (see McLaughlin 1997:435), and gill structure (see McLaughlin & de Saint Laurent 1998: 161). The submedian grooves on the shield are termed "paragastric grooves" (see Ko- mai & Osawa 2001:1291). Forest et al. (2000:24) is followed in the interpretation of the ocular peduncle, which is provided basally with a small calcified plate referred to as the "ocular acicle". The sternites of the third maxillipeds and third and fifth pe- reopods are each shown as "third", "sixth", and "eight" thoracic sternites. Shield length (si), as measured from the tip of the rostrum to the midpoint of the pos- terior margin of the shield, indicates spec- imen size. The lengths of the segments of the chelipeds were measured along the dor- somesial margin except for the chelae, which were measured along each the dorsal midline from the proximal margin of the palm to the level of the distal tip of the