PROC. BIOL. SOC. WASH. 98(3), 1985, pp. 711-717 APONOMMA ELAPHENSE PRICE, 1959 (ACARI: IXODIDAE): DIAGNOSIS OF THE ADULTS AND NYMPH WITH FIRST DESCRIPTION OF THE LARVA James E. Keirans and William G. Degenhardt Abstract. — The larva of Aponomma elaphense is described, diagnostic char-acters for the male, female, and nymph are given and scanning electron photo-micrographs are provided for all stages. Range and habitat information is provided for the only known host of A. elaphense, Elaphe subocularis, the Trans-Pecos rat snake. Worldwide, there are approximately 21 species in the genus Aponomma, only two of which are found in the Western Hemisphere, A. quadricavum Schulze, found in Haiti and Cuba (Schulze 1941; Cerny 1966), and A. elaphense Price, found in Texas, parts of New Mexico and northern Mexico (Price 1959; Degen-hardt and Degenhardt 1965). During examination of a series of the Trans-Pecos rat snake, Elaphe subocularis, the only known host of Aponomma elaphense, one of us (W.G.D.) collected numerous adults, nymphs, and previously undescribed larvae of that tick (De-genhardt, in press). We give a diagnosis of the male, female, and nymph of A. elaphense, illustrating key characters with scanning electron photomicrographs (SEM) and describe the previously unknown larva. Specimens were prepared for SEM by the method of Corwin et al. (1979). Aponomma elaphense Price, 1959 Diagnosis — male (Figs. 1-6).— A very small Aponomma, ca. 2.00 mm long (excluding capitulum) ca. 1.85 mm wide; inornate, light brown. Scutum (Fig. 1) smooth, without cervical or marginal grooves, setae and punctations minute, inapparent under binocular microscopy. Capitulum dorsally (Fig. 2) subtriangular, lacking cornua; ventrally (Fig. 3) with hypostomal dentition 2/2 throughout, api-cally with a large corona of fine denticles; palpi elongate. Legs (Figs. 4, 5) each with a single triangular spur on coxae I-IV; Haller's organ roof slit-like and slightly bifurcate medially, 5 anterior pit setae. Spiracular plate (Fig. 6) suboval with a long narrow dorsal prolongation, goblet cells minute. Diagnosis —female (Figs. 7-12).— Small, suboval, ca. 2.40 mm long (excluding capitulum) ca. 2. 1 5 mm wide; inornate, light brown. Scutum (Fig. 7) broader than long, cordiform, smooth, without cervical grooves, setae and punctations minute. Capitulum dorsally (Fig. 8) subtriangular, cornua absent; porose areas subcircular, shallow; ventrally (Fig. 9) with hypostomal dentition 2/2 [although the hypostome figured has a single supernumerary tooth between file one and two on the left side of the hypostome as viewed from above]; palpi elongate. Legs (Fig. 10) with coxae as in male. Genital aperture (Fig. 1 1) at level of coxae II. Spiracular plate (Fig. 12) suboval with a short dorsal prolongation, goblet cells minute.