READY & LAINSON (1982) referred to speculation over the identity of the sand fly which first experimentally transmitted a neotropical Leishmaniu by bite (STRANGWAYS-DIXON & LAINSON, 1962; 1966). Previously published comments on this fly’s identity (WILLIAMS, 1970; WILLIAMS & COELHO, 1978) were based on examinations of the actual specimen and after comparing it with other species of the same subgenus. The Department of Entomology, British Museum (Natural History), which received the specimen in December 1967, recently loaned me the material. In addition to studies on the fly made at the Gorgas Memorial Laboratory, Panama, and at BM(NH), it has now been possible to compare the fly with specimens in the Belo Horizonte reference collection of Phlebotominae. For simnlicitv’s sake. the fly in question is, herein, called “the Belize specimen”. It is impossible to identify the Belize specimen to specific level because it lacks spermathecae, spermathecal ducts and the genital fork. However, from the appearance of certain non-sexual features, the Belize specimen cannot belong to two species of the same subgenus Psychodopygus collected in Belize between 1963 and 1969 (WILLIAMS, 1970), and some species mentioned by READY & LAINSON (1982) can be eliminated. Thoracic pigmentation: The mesoscutum, mesoscutellum and postnotum of the Belize specimen are moderately but distinctly infuscated, and clearly contrast with the paleness of the thoracic pleura. It is unlikely that this colour contrast is an artefact due to distortion of the thorax. The pigment contrast on the thorax of the Belize specimen is similar to that of Lutzomyia (Psychodop$us) panamensis, L. (Ps.) geniculata (= L. (Ps.) guyanensis of some authors) and L. (Ps.) bispinosa, the three species of the subgenus collected in Belize in 1963-69. The Belize specimen, with a pale pronotum, differs from L. (Ps.) bispinosa, in which the uronotum is weaklv infuscate. The orocoxae of the Belize suecimen are as nale as the thoracic pleura. For this reason, the specimen cannot be identified as L. (Ps.) hirsuta nicaramrensis which has darkened procoxae in both sexes(FAIRCHILD & HERTIG, 1961.; YOUNG, 1979). Because of the contrast in thoracic pigmentation, the Belize specimen most certainly cannot be identified as L. (Ps.) carreirai thuZa (= Ps. -pessoanus of READY & LAINSON, 1982). In snecimens of L. (Ps.) carreirai thula. material from Panama and Colombia having been’examined, the entire thorax is pale, or almost so, and there is no noticeable difference in thoracic pigmentation. On the basis of thoracic pigmentation, it can be deduced that the Belize specimen cannot be L. (Ps.) carreirai thula, L. (Ps.) hirsuta nicaraguensis or L (Ps.) bispinosa. Cibarium: The cibarial arch in the Belize specimen and L. (Ps.) pana memis is well defined and complete. In L. (Ps.) geniculata and L. (Ps.) bispinosa, the cibarial arch is not well defined but appears to be complete. The cibarial arch of L. (Ps.) carreirai thula is so weakly defined that it is best described as incomplete. The cibarial pigment patch in the Belize snecimen. L. (Ps.) panamensis and L. (Ps.) geniculata is fairlv ‘well‘ defined and annears as a’ “m it seems to be triangular in shape. The salivary pump in the Belize specimen, L. (Ps.) panamensis and L. (Ps.) bispinosa is roughly circular in optical section and smaller than the pump in L. (Ps.) geniculata and L. (Ps.) carreirai thula, both having an oval-shaped pump along a distal-proximal axis. From the general appearance of the cibarium, it can be concluded that the Belize specimen cannot be identified as L. (Ps.) carreirai thula. L. (Ps.) eeniculata or L. (Ps.) bispinosa. I ~ , ”