252 Memoir Sears Foundation for Marine Research 



seum; an immature male, 282 mm long, from Lat. 27°27' N, Long. 96°i7' W, 65 

 fathoms, Oregon St. 158; 2 males and 2 females, 230— 310mm long, Lat. 30°02'N, 

 Long. 86°53' W, 60 fathoms, Oregon St. 332, and two males each of 310 mm, from 

 Lat. 30°02'N, Long. 86°55' W, 64 fathoms, Oregon St. '},(^'t^. 



Distinctive Characters. Raja olseni closely resembles R. laevis in general appearance 

 and in lacking thorns along the midbelt of the disc from the level of the axils of the 

 pectorals to the vicinity of the spiracles. But it differs from laevis in having an inter- 

 space between the dorsal fins nearly or quite as long as the base of the first dorsal (only 

 0.1—0.3 that long in laevis) and by having a fringe on the expanded outer margin of 

 the nostril (smooth in laevis); also, the lateral folds along its tail extend only to the 

 anterior third of the caudal fin, whereas in laevis they extend almost or quite to the 

 extreme tip of the tail; the lower sides of its disc are prickly along the anterior edges 

 and over the rostral cartilage (smooth on laevis of equal size), and its mucous pores 

 are not marked with black as they are in laevis. It differs from R. spinicauda in its 

 fringed nostril lobe, in its shorter tailfolds, in the interspace between its dorsals, and 

 in having three rows of thorns on the tail (only one row on spinicauda). 



Description. Proportional dimensions in per cent of total length. Male, 280 mm 

 (U. S. Nat. Mus., type, No. 153556), and male, 282 mm (Harv. Mus. Comp. ZooL, 

 No. 37176), from the northwestern part of the Gulf of Mexico. 



Disc: extreme breadth 69.0, 72.0; length 54.0, 58.2. 



Snout length: in front of orbits 15.6, 17.4; in front of mouth 17.7, i9-5. 



Orbits: horizontal diameter 4.4, 4.3; distance between 3.6, 4.3. 



Spiracles: length 2.0, 2.3; distance between 6.3, 6.7. 



Mouth: breadth 7.9, 8.2. 



Nostrils: distance between inner ends 7.9, 8.3. 



Gill openings: lengths, ist 2.0, 2.0; 3rd 2.1, 2.1 ; 5th 1.6, 1.6; distance between 

 inner ends, ist 13.6, 14.2; 5th 7.3, 8.2. 



First dorsal fin: vertical height 2.5, 2.5; length of base 4.3, 4.4. 



Second dorsal fin: vertical height 2.4, 2.3; length of base 4.6, 4.4. 



P^/w'c5; anterior margin 13.2, 13.5. 



Distance: from tip of snout to center of cloaca 47.5, 49.3 ; from center of cloaca 

 to 1st dorsal 30.4, 30.2; to tip of tail 52.5, 50.7; from rear end of 2nd 

 dorsal base to tip of tail 9.0, 7.8. 



Interspace between: ist and 2nd dorsals 4.3, 3.9. 



Disc about 1.3 times as broad as long, the maximum anterior angle in front of 

 spiracles about 90° ; anterior margins concave just posterior to tip of snout, weakly 

 convex opposite eyes and spiracles, thence about straight rearward; outer corners nar- 

 rowly rounded; posterior corners more broadly so; posterior margins gently convex. 

 Axis of greatest breadth about 67 °/o of distance rearward from tip of snout towards 

 axils of pectorals. Tail with a lateral fold low down on each side beginning posterior 

 to axils of pelvics by a distance about */& ^s long as eye and ending opposite anterior 



