Fishes of the IVestern North Atlantic 343 



Species. Recent surveys of the genus, as here defined, for various parts of the 

 world recognize a total of some 30 species." But it is likely that a general revision 

 would result in a considerable reduction in this number. Six species are known from 

 the western Atlantic (see Key, p. 343). 



The representatives oi Dasyatis and oi Himantura in the western Atlantic are more 

 readily identifiable by the proportionate dimensions of disc and tail and by the shape 

 of the disc than they are by the degree of development of the longitudinal ridges or 

 folds on the tail, though these last characters are more significant from the generic 

 standpoint. The local members of the two genera are therefore grouped together in 

 the following Key for convenience in identification. 



Key to North Atlantic, Western South Atlantic and Tropical West African 

 Species of Dasyatis and Himantura*^ 



I a. Anterior contour of median sector of disc either a uniform arc of long radius or 

 nearly straight. 



2 a. Distance from center of cloaca to origin of tail spine nearly as long as dis- 

 tance from center of cloaca to tip of snout; entire upper surface of disc closely 

 clothed with small tubercles; tail without folds above or below. 



Himantura schmardae (Werner) 1904, p. 390. 



2 b. Distance from center of cloaca to origin of tail spine much shorter than dis- 



tance from cloaca to snout; upper surface of disc mostly naked; lower surface 

 of tail with well developed longitudinal cutaneous fold. 



Dasyatis violacea (Bonaparte) 1832. 

 Mediterranean. 

 I b. Anterior contour of median sector of disc subangular, with tip of snout forming 

 the apex. 



3 a. Entire upper surface of disc rough with minute dense asperities. 



Dasyatis rudis (Giinther) 1 8 70. 

 Old Calabar, Equatorial West Africa.*'^ 



3 b. Upper surface of disc mostly smooth except along median belt, and here or 

 there elsewhere. 



4 a. Distance from level of axils of pectorals to origin of tail spine about as 

 long as distance from level of axils of pectorals to rear margins of orbits; 

 center of back with a single large white tubercle. 



Dasyatis margarita (Giinther) i 8 70. 

 Tropical West Africa. 



40. Garman, Mem. Harv. Mus. comp. Zool., j6, 1913: 381, 388, 392; Fowler, Bull. Amer. Mus. nat. Hist., 70 (i), 

 1936: 125; Bull. U.S. nat. Mus., 100 (/j), 1941: 413, 420, 421. 



41. China and Trinidad are given as localities for Dasyatis bennetti by Muller and Henle (Plagiost., 1841: 160), its 

 describers. But recent authors have restricted the name to the Pacific form, hence it is not included in the Key. 

 For references, see Fowler (Bull. U.S. nat. Mus., loo [/j], 1941: 413). 



42. Giinther, Cat. Fish. Brit. Mus., 8, 1870: 479. Thus far D. rudis appears to be known from the original account 

 only, which was based on a single large specimen 6^/2 feet broad. A more detailed account of this species is much 

 to be desired, especially as regards its tailfolds, if any. 



