50 BULLETIN 189, UNITED STATES NATIONAL MUSEUM 



Family RHINOBATIDAE: Guitarfishes 



Body depressed throughout; anterior part of body with pectorals 

 forming a disk, tapering forward; tail rather wide at base, with a 

 lateral dermal fold; spiracle large, immediately behind eye; nostril 

 oblique, wide; teeth in pavement; dorsal fins 2, both on the tail. 



A single genus is represented in the Peruvian collection. 



Genus RHINOBATOS Link, 1790 



Disk subtriangular, wide posteriorly, tapering forward into the 

 rather pointed snout; snout formed by a long rostral cartilage and a 

 large more or less translucent area on each side; the large spiracle 

 usually with two dermal folds, rarely with one or none, on its poste- 

 rior surface ; first dorsal behind ventrals ; no subcaudal lobe ; ventrals 

 close to pectorals. 



A single species is known from Peru. 



RHINOBATOS PLANICEPS Carman 



guitarra 

 Figure 8 



Rhinobaius planiceps Garman, 1880, p. 168, Peru and Galapagos Islands (original 

 description); 1881, p. 520, Paita and Callao, Peru; Galdpagos Islands 

 (description); 1913, p. 283, pi. 17a, figs. 3-4 (description). — Evermann and 

 Radcliffe, 1917, p. 12, pi. 2, fig. 3, Lobos de Tierra, Peru (description). — 

 Nichols and Murphy, 1922, p. 504, Pacasmayo, Peru. — Fowler, 1941a, p. 

 225 (references; range). — Beebe and Tee-Van, 1941, p. 251, fig. 6 (range; 

 field characters; size; references). 



Body depressed throughout; disk moderately broad, its width at 

 broadest point 1.05 to 1.2 in length anterior to axil of pectoral, or 2.75 

 to 3.1 in total length; length anterior to vent 2.3 to 2.45 in total 

 length; width of tail at axil of ventrals 3.2 to 4.5 in length anterior to 

 axil of pectoral, with a prominent lateral dermal fold; snout long, 

 moderately narrow, its lateral margins very slightly concave, its 

 length anterior to eyes 2.6 to 2.9 in length anterior to axil of pectoral, 

 its preoral length 2.2 to 2.6; rostral cartilage narrowest at midlength, 

 the ridges close together and parallel for fully half its length; longi- 

 tudinal diameter of eye slightly exceeding greatest diameter of spiracle, 

 3.8 to 5.4 in snout; interorbital 2.6 to 3.1 ; spiracle about as large as eye, 

 with a rudimentary fold on its posterior margin; nostril oblique, 

 larger than internarial space; mouth arched forward slightly in 

 middle; its width 1.95 to 2.2 in snout; teeth in jaws flat, in pavement; 

 median line of back at least to second dorsal with low keeled bucklers, 

 these also present on tip of snout, over superior orbital rim and at 

 shoulders, and on ridges of rostral cartilage in some specimens, ap- 

 parently more prominent in the young than in adults; dorsal fins of 

 approximately the same size and shape, highest anteriorly, distal 

 margins nearly straight, origin of the first about equidistant from 



