424 Memoir Sears Foundation for Marine Research 



the same time; while some are quite definitely pale-spotted and others are definitely 

 dark-meshed, still others exhibit various intermediate stages on different parts of their 

 discs, with dark striping extending radially toward the margins. Again, on some the 

 pattern may consist of a meshwork of broad bands whereas on others there are chains 

 of alternating dark dots and pale spaces on a background of intermediate shade. Or the 

 midzone of the disc may be plain brown while the outer belt is marked with darker 

 reticulations and pale bands, arranged longitudinally toward the central part of the disc 

 but radially toward the margins. On some specimens the dark markings take the form 

 of vermiculations rather than of a network or of stripes."" On some, the outer belt of 

 the disc is variegated by an irregular series of large roundish pale areas, while dark 

 cloudings, irregular in size or shape, may or may not involve the regions of the shoul- 

 ders, eyes, and spiracles. The inner parts of the pelvics have pale spots or dark reticul- 

 ations or vermiculations on a pale ground, and their outer margins are more or less 

 definitely dark-striped in radial pattern. 



The lower surface is yellowish, greenish or brownish white, the tail irregularly 

 marked with dark dots and larger spots; the outer zone of the disc has small dots of 

 the same hue as the dark areas on the back, either close along its extreme outer margin 

 only or extending inward over a band varying in breadth from specimen to specimen. The 

 pelvics are similarly dark-dotted below toward their posterior margins, combined in some 

 cases with an irregular pattern of dark radial stripes. The lower surfaces of the claspers 

 are plain whitish in some specimens but variously dark-spotted in others. No evidence 

 has been reported of adaptive changes in the color pattern on different backgrounds. i"! 



Relationship to Extralimital Species. Among Rays of the Pacific Coast of America, 

 U.jamaicensis resembles U. halleri most nearly. Indeed, we have found no sharpcut 

 criterion by which newborn specimens of the two can be separated with certainty. 

 However, quarter-grown specimens and larger are made easily identifiable as one or the 

 other by the fact that the midzone of the back, from the level of the front of the eyes 

 rearward to the tail spine, is rough with low tubercles on U.jamaicensis but perfectly 

 smooth on U. halleri. A less obvious difference, seemingly as reliable, is that the disc is 

 a little longer than broad in half-grown and larger specimens of U.jamaicensis but about 

 as broad as long in U. halleri. 



Among western Pacific urolophids, U.jamaicensis is paralleled by U. armatus 

 Miiller and Henle 1841 of the Bismarck Archipelago in the roughness of its back. 

 But the two species differ in shape, U. armatus having a pointed and prominent snout, 

 a disc rectilinear in anterior outlines, dermal armature consisting of small prickles, and 

 a single large median tubercle over the pectoral girdle. i''^ 



100. Three specimens of this type were christened 'vermiculatus var. nov. by Garman and were beautifully pictured by 

 him (Mem. Harv. Mus. comp. Zool., j6, 1913: 402, pi. 29). But in all respects other than the color pattern, they 

 are typical U.jamaicensis, hence they appear to represent merely an extreme color-variant of the latter. 



loi. An allied Australian species, Trygonoptera testacea Miiller and Henle 1S41, failed to show any adaptive changes in 

 tint on a black background, although its melanophores expanded after the injection of pituitary extract (Griffiths, 

 Proc. Linn. Soc. N. S. W., 61, 1926: 318). 



102. For firsthand descriptions of the type specimen of U. armatus, see Miiller and Henle (Plagiost., 1841 : 174), and 

 Dumeril (Hist. Nat. Poiss., j, 1S65: 628). 



