372 Memoir Sears Foundation for Marine Research 



tails intact are further separable from all of the foregoing, except D. say, by the presence 

 of a well developed longitudinal cutaneous fold along both the upper and lower sur- 

 faces of their tails. D. sabina resembles T). guttata somewhat in the shape of the ante- 

 rior part of its disc, but the former is easily recognized from the latter by: its deeply 

 concave nasal curtain (cf. Fig. 88 D with 86G); the more broadly rounded outer cor- 

 ners of its disc; the presence of a cutaneous tailfold above as well as below; and, in the 

 case of half-grown specimens or older, the tubercle-strewn area on its disc is relatively 

 much less extensive, and the mid-dorsal tubercles on the base of the tail are not notice- 

 ably larger than those on the posterior part of the disc. 



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

 Male, 229 mm broad, and female, 348 mm broad, from Florida (Harv. Mus. Comp. 

 Zool., Nos. 125 and 84 respectively). 



Disc: vertical length 96.7, loi.o. 



Snout length: in front of orbits 25.3, 26.7; in front of mouth 26.2, 26.1.*"^ 



Orbits: horizontal diameter 7.0, 7.0; distance between 9.6, lo.o. 



Spiracles: length 5.7, 6.6; distance between 15.3, 18.1. 



Mouth: breadth 8.3, 8.9. 



Exposed nostrils: distance between inner ends 9.8, 9.8. 



Gill openings: lengths, ist 2.8, 3.7; 3rd 3.1, 3.7; 5th 2.2, 2.6; distance between 

 inner ends, ist 19.2, 21.8; 5th 11.8, 13.8. 



Pelvics: anterior margin 20.5, 17.8. 



Distance: from tip of snout to center of cloaca 87.5, 93.0; from center of cloaca 

 to origin of caudal spine 50.7, 46.0. 



Disc in both sexes rhomboid, varying from about as long as broad to a little 

 broader than long (maximum about i.i times as broad as long); snout projecting as 

 a broad-based triangle with pointed tip; maximum anterior angle in front of spiracles 

 about 107-122°; outer corners broadly rounded and posterior margins moderately 

 convex; anterior margins concave (in varying degree) opposite eyes and spiracles. 

 Axis of greatest breadth about 45 "/o of distance rearward from snout toward poster- 

 ior limits of disc. Tail noticeably depressed dorsoventrally and oval in cross section 

 anterior to spine but approximately round posterior to spine; extremely slender toward 

 tip; more or less of the posterior part often lost, the remaining part more or less 

 thickened posterior to spine with healing of terminal wound; upper surface of tail 

 with a low but definite membranous fold or thin-edged keel varying in prominence 

 from specimen to specimen, originating about under tip of tail spine and extending 

 rearward for a distance about as great as that between outer margins of orbits ; hardly 

 more than a ridge in newborn specimens, but usually only a little narrower than height 

 of tail at midpoint of fold on adults; lower surface of tail with a similar but longer and 

 usually somewhat broader fold originating a little posterior to origin of tail spine and 



109. In two females and a male, with shorter snouts and with discs 187 to 292 mm broad, from Florida, the length in 

 front of orbits was only 20.6-21.9, that in front of mouth 22.2-23.5. 



