114 Memoir Sears Foundation for Marine Research 



anterior outline of its disc, by the close proximity of its spiracles to its eyes, by its 

 much narrower mouth with labial cartilages at the corners (this may be felt readily 

 in the larger sizes), and by its much more rigid snout. From the local species of Ben- 

 thobatis it is distinguishable by the tuberculate margins of its spiracles, by the shape of 

 its caudal (cf. Fig. 25 A with 26B), by its larger and fully formed eyes, and by the 

 fact that the inner margins of its pelvics are free from the sides of the tail for some 

 distance anterior to their tips. 



Description. Proportional dimensions in per cent of total length. Female, 239 mm 

 long, from New Smyrna Beach, Florida (Harv. Mus. Comp. Zool., No. 36398). Male, 

 274 m long, from Rio de Janeiro (Harv. Mus. Comp. Zool., No. 643). 



Disc: extreme breadth 54.8, 51.3; length 51.0, 47.8. 



Snout length: in front of orbits 13.0, 11.3; in front of mouth 15.0, 13.0. 



Orbits: horizontal diameter 4.5, 4.0; distance between 5.9, 5.8. 



Spiracles: length 2.5, 2.2; distance between 7.7, 8.0. 



Mouth: breadth 4.5, 5.1. 



Exposed nostrils: distance between inner ends 6.1, 6.6. 



Gill openings: lengths, ist 1.5, 2.2; 3rd 2.1, 2.4, 5th 1.5, 1.8; distance between 

 inner ends, ist 13.2, 13.0; 5th 7.1, 7.5. 



First dorsal fin: vertical height 9.2, 9.9; length of base 7.5, 7.3. 



Second dorsal fin: vertical height 8.6, 9.9; length of base 7.5, 8.4. 



Pelvics: anterior margin 12.5, 15.0. 



Distance: from tip of snout to center of cloaca 52.3, 50.0; from center of cloaca 

 to 1st dorsal 26.5, 24.9; to tip of tail 47.7, 50.0. 



Interspace between: ist and 2nd dorsals 2.7, 4.7; 2nd dorsal and caudal 3.5, 4.7. 



Disc subcircular, its anterior contour varying from evenly arcuate to moderately 

 ovoid, its breadth usually a little greater than its length ^^^ and 49—55 "/o as great as total 

 length; posterior margins of pectorals moderately recurved in broadly rounded contour. 

 Tail from center of cloaca somewhat shorter to slightly longer (84—101 "/o) than dis- 

 tance from center of cloaca to tip of snout; rounded above and moderately flattened 

 below, each side with a narrow longitudinal cutaneous fold extending from about 

 opposite or a little anterior to midpoint of base of first dorsal to origin of caudal fin. 



Length of snout in front of orbits about 1.6—2.2 times as great as distance between 

 eyes, its length in front of mouth about twice as great as distance between outer ends 

 of nostrils; the two lateral ridges of the trough-shaped rostral cartilage firm to the touch 

 nearly to the anterior margin of the head. Orbits moderately prominent (this may not 

 be the case in preserved specimens). Eyes fully developed and about ^/g as long as 

 spiracles, oval, their horizontal diameter about 42—78 °/o as long as distance between 

 orbits. Spiracles close behind eyes, transverse or slightly oblique, squarish in shape 

 when expanded, the margin ringed with a single series of 12 to 20 low rounded papillae 



131. Among specimens in our Study Material, the ratios of breadth of disc to its length are from 1.01-1.08; in one 

 Brazilian specimen, probably of this species, this ratio was 0.99. See discussion of Narcine brachypkura Ribeiro 

 1923 (p. 123). 



