Fishes of the Western North Atlantic 345 



loa. A longitudinal cutaneous fold along lower side of tail 

 about as wide as height of tail ; upper surface of tail with 

 a low longitudinal ridge close posterior to spine, or at 

 least arched in cross section; sides of tail without con- 

 spicuous tubercles. 



Dasyatis americana Hildebrand and Schroeder 

 1928, p. 345. 

 lob. A longitudinal cutaneous fold along lower side of tail only 

 about half as wide as height of tail ; upper surface of tail 

 posterior to spine rounded, without longitudinal ridge; 

 sides of tail, in half-grown specimens and larger, rough 

 with conspicuous tubercles or thorns. 



Dasyatis centroura (Mitchill) 18 15, p. 352, and 

 Dasyatis aspera (Cuvier) 18 17. 

 Eastern Atlantic, tropical West Africa, Madeira, and Med- 

 iterranean.''* 



Dasyatis americana Hildebrand and Schroeder 1928 

 Figures 81, 82 



Study Material. Fifteen specimens, 126—525 mm wide, including embryos, from 

 Brazil, Trinidad, Puerto Rico, Cuba, Bahamas, Gulf of Campeche, Yucatan, Texas, 

 Florida, and Chesapeake Bay, in Museum of Comparative Zoology and U. S. National 

 Museum. 



Distinctive Characters. D. americana, regardless of size, is separable at a glance 

 from D. sabina, D. guttata and Himantura schmardae by the shape of the anterior part 

 of its disc (cf. Fig. 81 with 86, 88, 93). It is separable from H. schmardae also by the 

 position of its spine well forward on the tail (cf. Fig. 81 with 93). It is distinguished 

 further from D. guttata by the fact that the armature on the dorsal crest of its disc on 

 either side of the midline of tubercles consists only of minute prickles. If the tail is 

 intact, D. americana has only a low ridge on its upper surface, whereas D. say has a 

 well developed fold there. Specimens of D. americana that have lost their tails are 

 separable from D. say by the fact that both the outer and the posterior corners of 

 their discs are much more abrupt than those of the latter (cf. Fig. 8 i with 90). The 

 relatively great breadth of the lower tailfold of D. americana (cf. Fig. 8 i A with 83 A), 

 plus the presence of a ridge or keel on the upper surface of the tail posterior to the 

 spine, marks it off from D. centroura. Apart from the size, a tailless D. americana, prior 

 to the appearance of the mid-dorsal thorns, resembles a young D. centroura so closely 

 that we have been unable to find any dependable criteria by which to distinguish the 

 one from the other. Even so, the danger of confusing them is small, for D. centroura 



44. It is still an open question whether or not D. centroura of the western Atlantic and D. aspera of the eastern are 

 separable; for discussion, see p. 357. 



