PROC. BIOL. SOC. WASH. 101(2), 1988, pp. 438-443 ROBINSICHTHYS ARROWSMITHENSIS, A NEW GENUS AND SPECIES OF DEEP-DWELLING GOBIID FISH FROM THE WESTERN CARIBBEAN Ray S. Birdsong Abstract. —Robinsichthys arrowsmithensis is described from Arrowsmith Bank in the western Caribbean. The genus is among the deepest dwelling gobiids with some specimens taken below 240 m. The diagnostic characters and mon-ophyly of the tribe Gobiosomini are discussed. Robinsichthys is assigned to the Gobiosomini; however, its relationship to other gobiosominines is unclear. The difficulty and expense of collecting on deep, rough-bottom habitats makes their faunas among the most poorly known in the sea. In 1 967-1 968, the University of Miami research vessels R/V John Elliott Pillsbury and R/V Gerda made two brief collecting forays, comprising five 3 m otter-trawl sta-tions, in depths ranging from about 90 to 585 m on Arrowsmith Bank. The bank, a submarine prominence northeast of the is-land of Cozumel off the coast of Yucatan, is centered at approximately 21°05'N, 86°30'W. Along its western margin, the bank drops precipitously from depths of approx-imately 20 m to over 4000 m in the adjacent Yucatan Channel. The waters are of tropical oceanic clarity and it is apparent that the live-bottom habitat extends to a consider-able, but undetermined, depth. The limited material obtained includes an unusually large proportion of undescribed or poorly known species of fishes, crustaceans, and mollusks. Among the fishes collected was the gobiid, Robinsichthys arrowsmithensis, herein described as new. Methods and materials . — Counts and measurements were made following Bohlke & Robins (1968) except as noted. Measure-ments are straight-line distances made with an ocular micrometer and converted to the nearest 0. 1 millimeter. Morphometric data are presented in thousandths of standard length (SL). Gill-raker counts are from the first ceratobranchial plus first epibranchial. Vertebral counts, spinous dorsal-fin pteryg-iophore formulae (DF), and number of anal pterygiophores preceding the first haemal spine (AP) were determined from radio-graphs or cleared and stained material and follow the conventions and notational pro-cedures of Birdsong et al. (1988). Institu-tional abbreviations used are: UMML, Uni-versity of Miami, Rosenstiel School of Marine and Atmospheric Sciences; USNM, National Museum of Natural History, Washington, D.C. Robinsichthys, new genus Diagnosis.— Vertehrae 11 + 17 = 28; 7 spinous dorsal-fin pterygiophores, the last with or without a spine; cephalic lateralis pores absent; pelvic fins separate to base, rays branched with fifth ray longest; caudal fin with hypurals 1-2 fused to each other but free from hypurals 3-4 and the terminal vertebral element; one epural; body scaled posterior to pectoral axil with 25-28 ca-ducous scales; caudal fin with at least one highly modified scale (Fig. 1) on base of upper primary rays, lower base probably also with a modified scale but none remain in the specimens; two anal pterygiophores pre-ceding first haemal spine (vertebra 1 2); epi-pleural ribs present on vertebrae 1-9, pleu-ral ribs on vertebrae 3-10; metapterygoid
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