272 Memoir Sears Foundation for Marine Research 



tween 91 and 127 fathoms and at a temperature between 0.65 and -1.5° C, in collec- 

 tion of Newfoundland Department of Natural Resources. Also two egg-cases, appar- 

 ently of this species (p. 275), one with embryo from Banquereau Bank off Nova Scotia, 

 Lat. 44° 1 5' N, Long. 58°03' W (source unknown), the other empty, from the conti- 

 nental slope off southwestern Georges Bank, Lat. 3 9° 5 3' N, Long. 69°oo' W, from 

 between 260 and 350 fathoms, trawled by the research vessel Caryn of the Woods Hole 

 Oceanographic Institution, September 11, 1949. 



Distinctive Characters. Although the upper surface of its disc and tail are more or 

 less prickly (see p. 274), R. spinicauda is set apart from all other members of its genus 

 in the western North Atlantic (Greenland to the Amazon) by the fact that its only large 

 thorns are in a single row of 2 1-26 extending from the level of the axils of the pelvics 

 rearward along the midline of the tail. In these respects it falls closest to R. laevis. How- 

 ever, adult specimens of the two species are easily separable, for the tail of R. spinicauda 

 bears only the single median row of thorns whereas that of R. laevis bears three rows, 

 and while the mucous pores on the lower surface of R. laevis are marked with black pig- 

 ment dots or streaks, those of R. spinicauda are not so marked. 



Description. Proportional dimensions in per cent of total length. Male, 1,236 mm, 

 from Lat. 48°47' N, Long. 52°47' W (specimen from Newfoundland Department Nat- 

 ural Resources). 



Disc: extreme breadth 68.0; length 56.6. 



Snout length: in front of orbits 17.8 ; in front of mouth 17.8. 



Orbits: horizontal diameter 2.8; distance between 4.9. 



Spiracles: length 3.0; distance between 7.3. 



Mouth: breadth 8.1. 



Nostrils: distance between inner ends 7.4. 



Gill openings: lengths, ist 1.4; 3rd 1.5; 5th i.i; distance between inner ends, 



1st 15.7; 5th 12.4. 



First dorsal fin: vertical height 2.0; length of base 3.3. 



Second dorsal fin: vertical height 2.0; length of base 3.0. 



Pelvics: anterior margin 8.6. 



Distance: from tip of snout to center of cloaca 52.7; from center of cloaca to 

 1st dorsal 37.1 ; to tip of tail 47.3; from rear end of 2nd dorsal base to tip 

 of tail 2.9. 



Interspace between: ist and 2nd dorsals 1.2. 



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

 about 95°; tip of snout subangular or slightly blunted; anterior outlines nearly straight 

 rearward to level of spiracles, then bulging a little outwardly and following a sinuous 

 outline that is weakly concave and next weakly convex toward outer corners; outer 

 corners rather abruptly rounded, posterior corners much more broadly so; posterior 

 margins weakly convex. Tail with narrow lateral folds extending nearly its entire length, 

 at line of transition from rounded upper surface to flat lower surface; its length from 



