Fishes of the Western Nort/i Atlantic 7 1 



resembles R. cemiculus the most closely. But there is no danger of confusing young 

 specimens of the two, for R. cemiculus has a row of sharp spines along each rostral 

 ridge whereas R. ferccllens does not. Older R. percellens appear to be separable from 

 R. cemiculus by a somewhat shorter nostril relatively, by a larger number of tubercles 

 in the mid-dorsal row (only about 17—20 in R. cemiculus, see p. 50, footnote 26), by 

 somewhat more prominent spiracular folds, by somewhat lower dorsals relative to their 

 lengths, by less prominent tubercles on the shoulders, and usually by the pale-spotted 

 and dark-clouded upper surface (R. cemiculus is plain-colored above). 



R. percellens, when fully grown, resembles R. productus of the Pacific Coast of 

 Mexico and California, but it is separable from R. productus by the fact that the origin 

 of its first dorsal is posterior to the tips of the pelvics by a distance about as great as 

 the distance between the outer ends of its spiracles (less than half that great in R. pro- 

 ductus). Less conspicuous differences are: tubercles in median row more regular in R. 

 percellens, mouth a little less arched, and nostril a little shorter. Young of the two differ 

 more noticeably; those of R. percellens have more numerous but much smaller mid- 

 dorsal thorns and lack the fleshy fringe on the upper tip of the snout, a feature that 

 is conspicuous in the young of R. productus. However, it is not until later in growth 

 that the difference in the position of the first dorsal relative to the pelvics develops in 

 the two. Also, R. productus is considerably the larger of the two, growing to a length 

 of more than four feet. 



Size. The claspers of one male in our Study Material, 560 mm long (about 22 in.), 

 appear to be fully developed or nearly so. The largest specimens reported were 31^" 

 and about 39 inches^i long. 



Developmental Stages. A young female, 210 mm long, resembles the adult closely 

 in general form and has 43 enlarged tubercles in the midline to the first dorsal, 10— i i 

 between the first and second dorsals, 2—4 in front of each orbit, 3—5 around the inner 

 orbital margin to the inner end of each spiracle, and 2—3 on each shoulder. The tubercles 

 in the midline are more uniform in size and are rather more thorn-like in shape than 

 in the adult, though not appreciably larger. The tip of the snout does not bear a fleshy 

 fringe, such as that which characterizes the young of R. productus of the Pacific Coast 

 of Mexico and California. 



Habits. In Uruguayan waters it is taken on sandy bottom throughout the year 

 down to a depth of iio meters.*^ Nothing more is known of its habits. 



Range. Coastal waters of the western Atlantic from northern Argentina to the 

 Caribbean; also reported off" tropical West Africa (Dahomey and mouth of the Congo).** 



Occurrence in the Western Atlantic. This Guitarfish is generally distributed from 

 about Lat. 38° S to the Caribbean; it has been reported from: Puerto Quequen, Mar 

 del Plata, and Buenos Aires, Argentina; from the vicinity of Montevideo and from 

 Maldonadoj Uruguay; from Santos, Rio de Janeiro, Pernambuco, Bahia, Ilha S. 



60. Miiller and Henle, Plagiost., 1841: 416, as Rkinobatus undulatus. 



61. Kner, Novara Exped., Zool., i, Fische, 1865: 416, as Rkinobalus undulatus. 



62. Devincenzi, An. Mus. nac. Montevideo, (2) i (4), 1920: 126. 



63. For West African references, see Fowler (Bull. Amer. Mus. nat. Hist., yo [i], 1936: loi). 



