380 Memoir Sears Foundation for Mari?ie Research 



D. centroura of corresponding sizes. But the posterior corners of the disc are much 

 more broadly rounded in D. say than in either Z). americana or centroura; also, in Z). say 

 the distance between the inner ends of the second pair of gill openings is invariably 

 somewhat longer than the distance from the front of the lower jaw to the tip of the 

 snout, whereas in D. americana it is appreciably less than that, and in Z). centroura it is 

 only about as long as the length of the snout in front of the mouth. The smoothness and 

 regularly angular anterior contour of the discs of T). say that have lost their tails separate 

 them sharply from Himantura schmardae, in which the disc is covered with small tu- 

 bercles (p. 392) and is regularly arcuate anteriorly. 



Description. Proportional dimensions in per cent of extreme breadth of disc. 

 Male, 285 mm wide, from Florida (Harv. Mus. Comp. Zool., No. 36402). Female, 

 780 mm wide, from Rio de Janeiro (Harv. Mus. Comp. Zool., No. 991). 



Disc: vertical length 85.4, 89.7. 



Snout length: in front of orbits 14.9, 16.8; in front of mouth 16.8, 15.9. 



Orbits: horizontal diameter 6.5, 6.0; distance between 9.1, 9.2. 



Spiracles: length 7.4, 8.2; distance between 16.8, 16.7. 



Mouth: breadth 7.7, 9.0. 



Exposed nostrils: distance between inner ends 8.8, 9.0. 



Gill openings: lengths, ist 3.3, 3.7; 3rd 3.3, 4.3; 5th 2.3, 2.7; distance between 

 inner ends, ist 19.7, 23.6; 5th 13.0, 15.8. 



Pelvics: anterior margin 17.9, 17.3. 



Distance: from tip of snout to center of cloaca 77.6, 82.7; from center of cloaca 

 to origin of caudal spine 34.0, 38.5. 



Disc rhomboid, i.i — 1.2 times as broad as long in both large and small spe- 

 cimens; snout hardly projecting from general contour ;i^' maximum anterior angle in 

 front of spiracles about 130°; the anterior margins nearly straight or weakly convex; 

 outer corners rounded, but much more narrowly so than in D. sabina; posterior mar- 

 gins weakly convex, increasingly so rearward; posterior corners broadly and evenly 

 arcuate. Axis of greatest breadth 35—40 % of distance rearward from tip of snout 

 toward posterior limits of disc. Tail moderately depressed dorsoventrally anterior to 

 spine, thus oval in cross section; circular in cross section from spine to rear end of 

 lower tailfold; slightly depressed thence rearward; upper tailfold originating either a 

 little anterior to tip of tail spine when latter is laid back or under it, depending on 

 length of spine, increasing gradually to maximum width about midway of its length 

 and then decreasing rearward to merge insensibly with general outline of tail; maximum 

 width of upper fold about equal to thickness of tail at same point; its length about 

 2.5 times as great as distance between spiracles; lower tailfold nearly uniform in width 

 throughout most of its length, its maximum width a little greater than thickness of 

 tail at same point and a little greater than width of upper fold; origin of lower fold 



127. D. say falls with D. americana and D. centroura in this respect and differs correspondingly from D. sahina and 

 D. guttata. 



