410 Memoir Sears Foundation for Marine Research 



1.8 times in females; tip of snout more or less blunted and projecting slightly from 

 general anterior contour; anterior angle from tip of snout to level of anterior margins of 

 orbits about 120—130° in males, 130—140° in females; anterior margins weakly convex 

 in front of general level of eyes, slightly concave opposite level of posterior edge of 

 spiracles, weakly convex again toward outer corners; outer corners narrowly rounded 

 or subangular; posterior margins weakly and evenly convex, their edges finely scal- 

 loped; posterior corners broadly rounded, merging insensibly into short and mod- 

 erately convex inner margin. Axis of greatest breadth about 55—60 "/o of distance back 

 from tip of snout toward rear limits of disc in females, about 60-70 "/o i" males. Tail 



Figure 98. Gymnura micrtira. A Dorsal view of tail of male, 420 mm wide, from Beaufort, North Carolina 

 (U. S. Nat. Mus., No. 51940), and B of male, 390 mm wide, from Willoughby Point, Virginia (U. S. Nat. 

 Mus., No. 25452) to show variations in color pattern, about 2.2 X- 



tapering, its length from center of cloaca 37-46 "/o ^s great as distance from center of 

 cloaca to tip of snout and about 1/4 (22-25 "/o) ^s great as width of disc; its lower sur- 

 face with a low longitudinal dermal ridge or keel, the upper surface with a similar but 

 somewhat more prominent keel, each extending along posterior two-thirds of tail. 



No tail spine at any age, this being one of the chief characteristics of the species." 

 Snout anterior to orbits about 70-80 "/o ^s long as distance between outer margins 

 of orbits in females, about equal to this distance in males; its length in front of mouth 

 about 1. 5-1. 7 times as great as distance between exposed nostrils in females, 2.0-2.1 

 in males. Spiracle about as long as orbit in small specimens but up to about 1.8 times 

 as long in large ones; its inner posterior margin perfectly smooth without trace of any 

 tentacular structure at any stage in growth. Anterior margins of gill openings sinuous; 

 first to third (longest) about 73-^4 as long as diameter of orbit; fifth gill openings only 

 about half as long as first to third; distance between inner ends of first pair about 



48. So far as we can learn, there is no published record of the presence of a tail spine on any specimen that can be re- 

 ferred with certainty to G. micrura. It has been stated repeatedly that large specimens may have tail spines, but 

 such reports hark back either to the original specimen of G. maclura (Lesueur) iSiy, which appears to have been 

 a G. altaruela (p. 406), or refer to other specimens so large that they almost certainly belonged to that species, not 

 to G. micrura. 



