Fishes of the Western North Atlantic 157 



part of each pectoral. But the pectorals of R. cyclophora are angular, hence they con- 

 trast sharply with the rounded outer contours of R. ackleyi. 



Description. Proportional dimensions in per cent of total length. Female, 231 mm, 

 from off Yucatan (U. S. Nat. Mus., No. 148290). Male, 410 mm, from Yucatan Bank 

 (Harv. Mus. Comp. Zool., type, No. 748). 



Disc: extreme breadth 63.0, 53.7; length ^2)-Si 48.0. 



Snout length: in front of orbits 15. i, 11.6; in front of mouth 17.7, 12.7. 



Orbits: horizontal diameter 4.3, 3.7; distance between 4.6, 3.9. 



Spiracles: length 2.6, 2.4; distance between 7.0, 5.8. 



Mouth: breadth 7.8, 7.5. 



Nostrils: distance between inner ends 8.7, 7.5. 



Gill openings: lengths, ist 1.9, 1.7; 3rd 1.9, 1.8; 5th 1.3, 1.2; distance between 

 inner ends, ist 15.4, 13.0; 5th 8.2, 7.3. 



First dorsal fin: vertical height 3.9, 2.2; length of base 7.7, 4.6. 



Pelvics: anterior margin 9.5, 10.4. 



Distance: from tip of snout to center of cloaca 48.2, 45.8 ; from center of cloaca 

 to 1st dorsal 31.6, 40.7; to tip of tail 51.8, 54.2. 



Interspace between: ist and 2nd dorsals 4.1, 2.3. 



Disc about 1.1-1.2 times as broad as long; maximum anterior angle in front of 

 spiracles 97° on male, 106" on female; anterior rays of pectorals extending about 60- 

 70 "/o of distance from level of front of orbits toward tip of snout, the latter not ap- 

 preciably projecting; anterior contour only weakly concave rearward from tip of snout 

 and then a little more deeply so opposite spiracles on male, but less so on female; outer 

 and posterior corners broadly rounded; posterior margins rather strongly convex. Tail 

 with a narrow fold beginning about an eye's length posterior to axil of pelvic on each 

 side and extending to tip; length of tail from center of cloaca to origin of first dorsal 

 0.7—0.9 times, to origin of second dorsal 0.9—1.0 times, and to tip i.i — 1.2 times as 

 great as distance from center of cloaca to tip of snout. 



A cluster of small thorns on tip of snout; an irregular patch in front of spiracle 

 with three or four along its inner edge; one thorn on each shoulder on larger (male) 

 specimen (not yet developed on smaller female); one or two rows of small thorns over 

 anterior part of rostral cartilage; inner edge of orbit with three thorns on smaller 

 specimen, the number increasing to about eight on mature male; midline of back 

 from nuchal region to first dorsal of smaller specimen with 27 thorns, the row inter- 

 rupted at first between scapular region and level of axils of pectorals but becoming 

 continuous later; thorns of midline increasing to 70—72 at maturity (about 20 anterior 

 to axils of pectorals), the larger roughly alternating with the smaller, decreasing generally 

 in size rearward; on partly grown specimens, each side of tail with one additional 

 irregular row of thorns of various sizes extending rearward from near axil of pelvic 

 to opposite second dorsal; large specimens with two such rows on each side of tail, 

 the uppermost row (developed the latest) extending from a little anterior to axils of 



