Potamotrygon tigrina, n. sp. Figures 1–6; Tables 1–2 Holotype. MUSM 39978 [ex. ANSP 182452], juvenile male, 495 mm TL, Río Nanay (Amazonas drainage), large beach (left bank) at village of Pampa Chica, 4.54 km west of Iquitos, Departamento Loreto, Peru, 03° 45 ’09” S, 073° 17 ’00” W, collected with a bag seine by M. Sabaj, C. Pérez, A. Bullard, O. Castillo & C. DoNascimiento, 8 March 2005. Specimen dissected dorsally and ventrally by A. Bullard to remove parasites (intestine, olfactory bulbs and gills fixed); caudal stings missing when captured (Figures 1 –3, 5, 6). Paratype. ANSP 191998, preadult female, 560 mm TL, Río Nanay, Iquitos, Departamento Loreto, Peru (specimen donated to Nathan Lovejoy by Richard Ross; specimen somewhat dry, color faded) (Figures 4, 6). Diagnosis. A species of Potamotrygon diagnosed by its unique dorsal color pattern, composed of a light to dark brown or blackish background color, with a tan, bright yellow or orange irregular, highly curved and convoluted vermiculate pattern over entire disc and base of tail region, extending posteriorly to about one-half of tail length (to close to level of caudal stings). Potamotrygon tigrina, n. sp., is further distinguished from all other species of Potamotrygon, except P. schroederi, by presenting the distal half of tail, from about caudal sting origin, with a sharply contrasted pattern of five to six solid dark brown to black bars and uniformly cream colored interspaces of more or less equal width. It is further differentiated from congeners, except P. schroederi, P. orbignyi, P. h u m e ro s a Garman, 1913, P. histrix (Müller & Henle, 1834) and P. m a r i n a e Deynat, 2006, by presenting a single developed angular cartilage that is about one-fourth hyomandibula length (as opposed to two developed angulars of similar size, or a single developed but very elongated angular close to one-half hyomandibular length in other congeners). Furthermore, in P. t i g r i n a, n. sp. (and P. schroederi), dorsal tail spines usually occur in two ...