Fishes of the Western North Atlantic 53 



characters, supposedly specific,^' are so completely intergrading that the genus stands 

 in urgent need of revision, which we are not in a position to attempt. 



The Guitarfishes of the western side of the Atlantic fall in the group in which the 

 snouts are relatively long, in which the anterior nasal flaps do not extend inward onto 

 the internarial space, and in which there are two folds on the posterior margin of the 

 spiracles. The great majority of western Atlantic specimens that have been described, 

 or that we have seen, are rather evidently in one or the other of the two following 

 categories. 



A. Those with a cluster of prominent tubercles on the tip of the snout and with 

 the rostral cartilage widening rather noticeably toward its tip. Specimens of this sort 

 which have the upper surface of the trunk and tail densely freckled with a large number 

 of small pale dots were the basis for the species lentiginosus Garman 1880, described 

 from Florida. But the color pattern proves to be less dependable as a specific character 

 than has been commonly assumed, for our Study Material includes both unmarked and 

 sparsely spotted specimens from Texas that agree with typical lentiginosus in their mor- 

 phological features. 



B. Those without prominent tubercles on the snout and with the rostral cartilage 

 widening less toward its tip; plain-colored or with indistinct dark markings, or with 

 pale spots fewer and larger than in Rhinobatos lentiginosus. The western Atlantic repre- 

 sentatives of this category, known from Panama and the West Indies southward to 

 northern Argentina, have been described as three species, R. percellens (Walbaum) 

 1792, R. horkelii (Miiller and Henle) 1841, and R. stellio (Jordan and Rutter) 1897. 

 The first two are separable by the characters listed on pp. 56, 58. But there appears 

 to be no distinction between R. stellio and R. percellens (p. 68),^' and it seems doubtful 

 whether a sharp line can be drawn between R. percellens and R. lentiginosus^ for we have 

 seen one young Texan specimen which had the spatulate rostral cartilage ol percellens 

 but which was plain-colored and had the rostral tubercles only faintly indicated (perhaps 

 not yet developed). On the other hand, we have seen a Jamaican specimen which was 

 typically R. percellens in coloration as well as in shape of rostral cartilage, but which had 

 the tip of the snout armed with two rounded tubercles. Clarification of this puzzling situa- 

 tion must await further study of the Guitarfishes from the coasts of the Gulf of Mexico. 



The group represented by the eastern Atlantic R. rhinobatos and its immediate 

 allies, in which the anterior nasal flap extends inward across the inner margin of the 

 nostril and so encroaches upon the internarial space (Fig. 12), has no known counter- 

 part in the western Atlantic. 



■vinei Norman (Ann. Mag. nat. Hist., [lo] 7, 1931: 352) from West Africa, with caudals pictured as_ bilobed,_ fal 

 properly in Rhinobatos according to Poll (Result. Sci. Exped. oceanogr. Beige Cot. Afr. Atlant. [1948-49], 1951: 



9'. 94)- 



38. Shape of snout and of rostral ridges; degree of inward extension of the flap-like expansions of the anterior margins 

 of the nostrils; number (one or two) and prominence of the folds on the posterior margins of the spiracles. 



39. The statement in the original account (Jordan and Rutter, Proc. Acad. nat. Sci. Philad., 4r), 1897: 91) that the 

 distance from the origin of the first dorsal to the origin of the second dorsal in K. stellio is equal to the distance from 

 the axil of the pectoral to the origin of the first dorsal, was an evident slip, for re-examination of the original spe- 

 cimen (for which we have to thank the Natural History Museum of Stanford University) shows that axil of the pelvic 

 was intended. 



