PROC. BIOL. SOC. WASH. 98(3), 1985, pp. 644-654 A NEW SPECIES OF PSILOGOBIUS FROM THE INDO-PACIFTC WITH A REDESCRIPTION OF PSILOGOBIUS MAINLANDI (PISCES: GOBIIDAE) Ronald E. Watson and Ernest A. Lachner Abstract. —The genus Psilogobius Baldwin is redescribed and now contains two species, P. mainlandi from the Hawaiian Islands and P. prolatus, new species, from the Great Barrier Reef, Australia and the Cocos-Keeling Islands, eastern Indian Ocean. Pronounced sexual dimorphism occurs in both species. In addition to the genital papilla, males have longer fins, longer filamentous first dorsal fin spines, longer upper jaws than the females, and differ in coloration. Psilogobius prolatus differs from P. mainlandi in having dark pigmentation on the upper jaw, the AITO sensory pore usually present, a small patch of tiny scales on upper operculum, pectoral fin rays less numerous, modally 15, longer dorsal, anal and caudal fins, a longer upper jaw and in certain sexual dichromatic marks or bars. Psilogobius mainlandi was originally described by Baldwin ( 1 972: 1 25) as mono-typic from specimens collected by G. B. Mainland in 1939 at Kaneohe Bay, Oahu, Hawaiian Islands. Mainland named the new species Paroxyurichthys edmondsoni and described it in his master's thesis that was never published. The name Pa-roxyurichthys edmondsoni was published by C. H. Edmondson (1946); however, Baldwin (1972:125) noted that there was no description or illustration and that the name constituted a nomen nudum. The first author, while examining recently captured Psilogobius from Hawaii, thought he had a new species. Further study revealed that these specimens were P. mainlandi but were not easily recognized since many important diagnostic features were overlooked or vague in Baldwin's account. A redescription of P. mainlandi from the Hawaiian Islands revealed a new species of Psilogobius from Australia and the eastern Indian Ocean. Methods Methods follow those of Lachner and Karnella (1980), and Lachner and McKinney (1974, 1978), except where indicated. The pterygiophore formula of the spines of the dorsal fin in relationship with the underlying vertebrae is after Lachner and McKinney (1974:875). Measurements were made with dial callipers in mm, and counts were taken from the left side unless noted otherwise. Mea-surements of fins follow Hubbs and Lagler (1958:25) except for the caudal fin which is measured from the central hypural base to the posterior tip of the longest ray. All proportional measurements are expressed to the nearest tenth of a percent of the standard length (SL), except for certain tabular data. Osteological aspects of the study were accomplished with radiographs, and cleared and alizarin stained specimens. In the descriptive accounts the values given for meristic characters pre followed
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