PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 1 L3(l):13-16. 2000. A new species of mud shrimp, Upogebia cortesi, from Pacific Costa Rica (Decapoda: Thalassinidea: Upogebiidae) Austin B. Williams t and Rita Vargas (ABW) National Marine Fisheries Service Systematics Laboratory, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A.; (RV) Museo de Zoologfa, Escuela de Biologfa, Universidad de Costa Rica, 2060 Costa Rica (t: deceased October 27, 1999) Abstract. — Upogebia cortesi, a new species of mud shrimp from the Pacific side of Costa Rica is described and illustrated. The type series was dredged parallel to shore in water of 30-40 m depth. The species shares lack of a strong proximal mesioventral spine on the merus of the second pereopod with several members of the genus from the western hemisphere; moreover, the species stands alone in having spineless articles on pereopods 1-5 except for fingers of the chelae. The rostrum has no ventral spines. Similarities between this and related species are emphasized in a partial abridgment of the key to upogebiid species in the eastern Pacific. Eight species of the family Upogebiidae have been reported for the Pacific coast of Costa Rica (Vargas & Cortes 2000). Of these Pomatogebia cocosia (Williams 1986) and Upogebia vargasae Williams, 1997, were described based on material from Costa Rica. During the 1998 Mollusk Workshop organized by INBio at the "Re-serva Absoluta de Cabo Blanco", Peninsula de Nicoya, a dredge sample conducted be-tween the mainland and Isla Cabo Blanco, at 30-40 m depth, yielded three specimens of a new species of Upogebia Leach, 1814, described here. The substrate where the specimens were obtained included calcare-ous algae and rock fragments; at least 10 species of brachyuran crabs and several mollusk species were also found in the sam-ple. Specimens are deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM), and in Museo de Zoologfa, Escuela de Biologfa, Universidad de Costa Rica, San Jose (UCRMZ), as indicated in the species ac-count. Upogebia cortesi, new species Fig. 1 Material. — Costa Rica, NW side of Isla Cabo Blanco, dredged parallel to coast, 30-40 m, 16-17 May 1998: USNM 291186, male holotype; UCRMZ 2220-06, male par-atope; USNM 291187, female ovigerous paratype. Diagnosis. — Rostrum with sides convex in dorsal view, obsolescent pair of spines on submedian anterior margin; projections to either side of rostrum slender and spine-like; no spine on postocular margin; ante-rior gastric region bearing many spines nearly hidden in patch of dense setae. Ab-dominal sternites unarmed. Telson subrect-angular, sides slightly crenulate. Merus of cheliped lacking subdistal dorsal spine and spines on ventral margin; carpus essentially spineless; palms spineless. Pereopods 2-5 spineless; pereopod 2 without proximal me-sioventral spine on merus. Description. — Rostrum (Fig. \a,b) hori-zontal in lateral view with tip slightly ex-ceeding eyestalks; convex in dorsal aspect, with pair of submedian obsolescent blunted
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