PROC. BIOL. SOC. WASH. 94(2), 1981. pp. 569-578 THE GENERIC STATUS AND DISTRIBUTION OF MONODELLA TEXAN A MAGUIRE, THE ONLY KNOWN NORTH AMERICAN THERMOSBAENACEAN Jan H. Stock and Glenn Longley Abstract. — Although the original description of Monodella texana Ma-guire, 1965, attributes several peculiar features, notably in the maxillipeds, to the sole North American representative of the Thermosbaenacea, a re-examination of material from the San Marcos area (Texas) revealed a close morphological similarity to European and West Indian taxa of Monodella, with which it clearly is congeneric. Maguire's (1964, 1965) discovery of the first thermosbaenacean outside the Mediterranean area awoke considerable interest by biogeographers and stygobiologists. Maguire attributed his material without comments to the genus Monodella, at that time only known from groundwaters in Italy, Yugoslavia, and Israel. Presently, the genus is known also from Spain, the Balearic Islands, France, and Greece, and outside the Mediterranean area from the British and U.S. Virgin Islands, Culebra (E. of Puerto Rico), Haiti, Cuba (references in Stock, 1976, and Stock, in press), Puerto Rico (unpub-lished personal observations) and Somalia (Messana, 1979). In the years following the description of the Texan thermosbaenacean, but preceding the discovery of extra-Mediterranean taxa, several carcinol-ogists wondered whether Maguire had been right in considering the New World taxon congeneric with the Old World species. When Stock (1976) described a second New World species, found in St. Croix (U.S. Virgin Islands), it became clear that true Monodellas existed outside the Medi-terranean, but at the same time doubt was cast on the correctness of Ma-guire's morphological observations. According to the original description, the Texan Monodella had a 2-segmented mandibular palp (versus 3-seg-mented in the other species), was devoid of endo-and exopodites on the 2nd maxilla (versus present), and fused coxo-and basipodal endites in the maxilliped (versus separate), and lacked maxillipedal epipodites (versus pres-ent). The most conspicuous difference between Maguire's description of M . texana and the other members of Monodella was the alleged presence, in the female, of a 2-segmented maxillipedal endopodite, whereas the normal female condition is characterized by the absence (or reduction to a vestigial setule) of an endopodite. The male maxillipedal exopodite of M. texana was described as 4-segmented, whereas 2-segmented is the normal situation.