-A new species of Atelopus from the Serrania de Sira, an isolated mountain range in central Amazonian Peru, is described. It is most similar to A. erythropus and A. tricolor from the Peruvian Andes, and A. andinus from the lowlands of eastern Peru. The new species can be distinguished from these similar species by having tan to dark brown color with small yellow warts on all dorsal surfaces, and by lacking light dorsolateral stripes. The Serrania de Sira is an isolated, moderately high mountain ridge (up to ca. 2400 m above sea level) in the upper Amazon basin of eastern central Peru. Limited collections in the late 1960s and early 1970s in this area revealed the presence of 17 anuran species, four of which are endemic (Duellman and Toft, 1979; Henle, 1992). In the late 1980s, comprehensive zoological surveys of the Serrania de Sira were undertaken by the University of Vienna (Henzl, 1991). Although the herpetological collection has been addressed only partially, to date two previously unknown endemic species have been discovered. One, a species of Dendrobates, was recently named by Aichinger (1991). The other belongs to the neotropical bufonid genus Atelopus and is described herein. MATERIALS AND METHODS The type specimens of the new species are deposited in the Naturhistorisches Museum Wien (NHMW). Specimens of other Atelopus examined for comparisons (listed in the Appendix) are in AMNH (American Museum of Natural History, New York), BM (British Museum (Natural History), London), CBF (Colecci6n Boliviana de Fauna, La Paz), KU (The University of Kansas, Natural History Museum, Lawrence), MNHNP (Museum national d'Histoire Naturelle, Paris), and ZFMK (Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn). Measurements are in millimeters (mm) and were taken with calipers to the nearest 0.1 mm. Abbreviations of measurements follow Gray and Cannatella (1985). In addition, we use SW for the sacrum width (see Coloma-Roman, 1997). Sex determination was by dissection. Atelopus siranus sp. nov. (Figs. 1-2) Atelopus sp.-Lotters, 1996: Figs. 26-27; Lotters and De la Riva, 1998:486. Holotype.-NHMW 33906:2 (field number MA 4667), adult male, collected in the Serrania de Sira, Departamento Huanuco, Peru, in 1988 by M. Aichinger. Paratopotype.-NHMW 33906:1 (field number MA 4648), same data as holotype. Diagnosis.-A small-sized Atelopus (SVL of two adult males 22.5 and 23.5 mm) which can be distinguished from all other known species of the genus by the following combination of characters: (1) slim body (SW/SVL 0.24-0.25; N = 2), with snout acuminate; (2) no neural spines externally visible; (3) long hind limbs, tibiotarsal articulation reaches before eye when leg adpressed forward along body (TIBL/SVL 0.48; N = 2); (4) foot shorter than tibia (FOOT/TIBL 0.820.84; N = 2); (5) tympanum absent; (6) small warts (no spiculae or coni) present on dorsal and lateral surfaces of body (including anterior portion of the head) and extremities, absent on ventral surface; (7) all toes (except Toe IV) fully webbed; (8) thumb short (THBL/HAND 0.440.46; N = 2); (9) plantar and palmar surfaces almost smooth, with poorly developed subarticular tubercles on some phalanges; (10) in preservative body uniform tan (dark brown with small yellow warts in life) above, lateral surfaces may be paler or darker (dorsolateral stripes lacking); venter uniform cream (in life reddish orange including plantar and palmar surfaces); limbs chocolate brown with tan (yellow in life) warts above and tan or yellowish cream (light yellow in life) spots below. In proportions, foot and hand morphology, and ventral coloration in life (reddish orange ventral surfaces), Atelopus siranus most resembles A. erythropus Boulenger and A. tricolor Boulenger, both from the Amazonian versant of the Cordillera Oriental in southeastern Peru. Atelopus andinus Rivero from the pre-Andean lowlands of eastern central Peru has similar proportions and shares some morphological charThis content downloaded from 157.55.39.55 on Tue, 23 Aug 2016 04:30:34 UTC All use subject to http://about.jstor.org/terms S. LOTTERS AND M. J. HENZL FIG. 1. Dorsal and ventral views of holotype of Atelopus siranus, NHMW 33906:2. FIG. 2. Right palm and left sole of holotype of Atelopus siranus, NHMW 33906:2. Line equals 2.0 mm. 170 This content downloaded from 157.55.39.55 on Tue, 23 Aug 2016 04:30:34 UTC All use subject to http://about.jstor.org/terms NEW ATELOPUS FROM PERU acters with A. siranus (i.e., foot, hand, and skin