The study of the pontoniid fauna of the Indo-West-Pacific region has resulted in the discovery of a number of undescribed species of the genus Periclimenaeus Borradaile, 1915. A revision of this genus, the second largest in the subfamily, at present in progress, cannot be completed for some time and it is considered advisable to provide preliminary descriptions of the species concerned, as has been done in the case of the genus Periclimenes Costa (Bruce, 1969). The brief descriptions and remarks given here will enable the species to be identified and may further contribute to their recognition in other parts of their ranges, pending their full description and illustration. All the specimens described are commensals of marine invertebrates. Most were obtained from sponges and some from tunicates. The hosts of most of the specimens were preserved and are in the process of identification. Periclimenaeus holthuisi sp. nov. Periclimenaeus rhodope, Holthuis, 1952: 125, fig. 54, 55, 55bis (not Coralliocaris (Onycocaris) rhodope Nobili, 1904). Remarks. — The species has been fully described by Holthuis, who noted a number of discrepancies between his specimens and Nobili's description. The examination of fresh material has provided specimens that correspond exactly with Nobili's description and indicate that Holthuis' material must be referred to a separate species, which is, of course, closely related to P. rhodope Nobili. Periclimenaeus holthuisi may be distinguished from P. rhodope by the following features: (i) posteriormost rostral tooth well behind orbital margin; (2) supraorbital spines less strongly developed; (3) basal segment