42 o Memoir Sears Foundation for Marine Research 



Urolophus jamaicensis (Cuvier) 1817^* 

 Figures 99, 100 



Study Material. Thirty-nine specimens," male and female, 120 to about 445 mm 

 long, late embryos to adults, from Cuba; Haiti; Trinidad; Jamaica; Old and New 

 Providence and Bimini in the Bahamas; Progresso, Yucatan; Key West, and south- 

 eastern Florida; in the U.S. National Museum and the Harvard Museum of Compar- 

 ative Zoology. 



Distinctive Characters. A well developed caudal fin extending around the tip of the 

 tail, combined with a formidable tail spine, mark Urolophus jamaicensis off from all other 

 Rays of the western Atlantic, except for its close relatives Urotrygon microphthalmum and 

 Urotrygon venezuelae. There is little danger of confusing it with the first of these, for 

 U. jamaicensis is arcuate in front, or at least very obtuse, the snout in front of the eyes 

 is only a little longer than the distance between the eyes, and its pelvics are rounded, 

 whereas Urotrygon microphthalmum is angular in front, the pointed snout is about twice 

 as long in front of eyes as the distance between eyes, and the pelvics are squarish with 

 angular corners {cf. Fig. 99 with loi). Obvious features that separate Urolophus jamai- 

 censis from Urotrygon venezuelae (which it resembles in appearance) are that its tail from 

 center of cloaca is shorter than its body from cloaca to snout (longer in Urotrygon 

 venezuelae), its disc is considerably narrower relatively, and the tip of its snout is less 

 prominent {cf. Fig. 99 with loi a). 



Description. Proportional dimensions in per cent of total length. Male, 328 mm 

 long from the Bahamas (Harv. Mus. Comp. Zool., No. 1153). Female, 375 mm long, 

 from near Palm Beach, Florida (Harv. Mus. Comp. Zool., No. 36399). 



Disc: extreme breadth 51.5, SS-S''' length 58.2, 59.7. 



Snout length: in front of orbits i i.o, 1 1.7; in front of mouth 1 1.9, 10.4. 



Orbits: horizontal diameter ^.^, 4.8; distance between 5.2, 4.5. 



Spiracles: length 4.0, 3.9; distance between 8.5, 8.3. 



Mouth: breadth 5.0, 7.2. 



Exposed nostrils: distance between inner ends ^.1,., ^.^. 



Gill openings: lengths, ist 1.8, 2.0; 3rd 2.0, 2.4; 5th 1.2, 1.3; distance between 

 inner ends, ist 11.6, 12.8; 5th 8.5, 9.3. 



Pelvics: anterior margin 10.7, 11.7. 



Distance: from tip of snout to center of cloaca 51.8, 53.8 ; from center of cloaca 

 to origin of caudal spine 26.8, 27.4; to tip of tail 48.2, 46.2. 



Disc about as broad as long in late embryos, but a little longer than broad after 

 birth (averaging about i .1 times as long as broad in series examined) ; ovoid in general 

 form, the anterior contour ranging from obtusely subangular with snout hardly project- 

 ing to almost evenly arcuate; lateral margins nearly evenly rounded, without any sug- 



96. For reasons why this name is used rather than U. sloani Blainville 1816, see p. 427, footnote 10. 



97. Including the types of the variety U. vermiculatus of Garman, 1913. 



