2 66 Memoir Sears Foundation for Marine Research 



Distinctive Characters. R. senta Is unique among hard-nosed Skates {Raja) of the 

 North and South Atlantic from the time it has grown to one-fourth its mature size^'* 

 in that the thorns on the tail dwindle in size rearward until those along the posterior 

 half to third are no longer distinguishable from the small prickles with which the tail 

 is generally clothed. Newly hatched specimens, in which this character is not yet 

 established, are separable from other hard-nosed Skates of the western North Atlantic 

 by the color pattern of the tail, which has two pale crossbars, each outlined anteriorly 

 and posteriorly by a dark band or blotch. They are set apart from the barred-tailed species 

 of Breviraja by the long rostral cartilage (reaching to tip of snout). 



Description. Proportional dimensions in per cent of total length. Female, 424 mm, 

 and male, 520 mm, from Emerald Bank, off Nova Scotia (Harv. Mus. Comp. Zool., 



No. 33919)- 



Disc: extreme breadth 62.0, 63.5; length 51.2, 50.5. 



Snout length: in front of orbits 15. i, 12.5; in front of mouth 15.3, 12.8. 



Orbits: horizontal diameter 4.2, 3.7; distance between 3.8, 4.0. 



Spiracles: length 2.6, 2.5; distance between 6.6, 7.1. 



Mouth: breadth 7.3, 8.1. 



Nostrils: distance between inner ends 7.3, 7.1. 



Gill openings: lengths, ist 1.9, 1.8; 3rd 1.8, 1.8; 5th 1.2, 1.3; distance between 



inner ends, ist 13.7, 13.7; 5th 7.5, 6.0. 

 First dorsal fin: vertical height 2.2, 2.6; length of base 5.4, 5.2. 

 Second dorsal fin: vertical height 2.4, 2.5; length of base 5.0, 6.1. 

 Pij/wVj; anterior margin 14.6, 13.6. 

 Distance: from tip of snout to center of cloaca 47.5, 46.5 ; from center of cloaca 



to 1st dorsal 38.7, 39.0; to tip of tail 52.5, ^2)-S'-> from rear end of 2nd 



dorsal base to tip of tail 3.3, 3.1. 

 Interspace between: ist and 2nd dorsals 0.0, 0.0. 



Disc about 1.2— 1.3 times as broad as long; maximum anterior angle in front of 

 spiracles about 110°; anterior margins nearly straight rearward from tip of snout in 

 adult females and in young of both sexes, but bulging moderately in front of level of 

 eyes in adult males; outer and posterior corners broadly rounded, posterior margins 

 strongly convex. Axis of greatest breadth about 70 "/o of distance back from tip of snout 

 toward axils of pectorals. Tail with lateral folds confined to posterior two-thirds and so 

 narrow that they are likely to be overlooked; its length from center of cloaca to first 

 dorsal about as great as distance from center of cloaca to tip of snout in small specimens, 

 decreasing in relative length with growth to about 80—90 "/o as great in adults; extreme 

 length of tail from center of cloaca about i.i times as great as length from cloaca to 

 snout in one-third-grown specimens and larger. 



Small specimens closely and uniformly prickly above on entire disc, on inner parts 

 of pelvics and on tail; 1—2 large thorns in front of orbit and as many behind it; 4—5 



138. It is also distinguishable from hard-nosed Skates of the Pacific Coast of America by the same character. 



