Fishes of the IVestern North Atlantic 425 



19/21?. The condition of the claspers suggests that males become sexually mature 

 at a width of about 150— 160 mm. ""^ The largest specimens reported thus far (from 

 Key West, Florida)!"^ were 305—355 mm wide, or about 600-670 mm long. 



Developmental Stages. Relative to their length, the discs of embryos are a little 

 broader than those of adults. Embryos also differ from their parents in their wholly 

 naked skins (see pp. 419, 422). However, the most interesting embryonic feature is the 

 presence of a well developed fleshy lobe or tentacle on the inner margin of each spiracle 

 close behind the eye. It is about as long as the spiracle itself and is directed outward 

 across the latter so that it conceals most of the spiracular opening."^ But it appears that 

 this lobe is resorbed either just before birth or shortly thereafter, for it is represented 

 by only a low swelling or knob on even the smallest of the free-living specimens that 

 we have examined. This embryonic structure is characteristic of other species of 

 Urolophus, and of Urotrygon as well, for we have found it equally developed on em- 

 bryos of Urolophus hallert Cooper 1863 from southern California and on those of 

 Urotrygon aspidurus (Jordan and Gilbert) 1881 from Panama. There is no dorsal fin 

 on the embryos of Urolophus jamaicensis examined, or on those of Urotrygon aspidurus, 

 but one is sometimes present on embryos of Urolophus cruciatus (Lacepede) 1804"^ of 

 Australia. 



Females of U. jamaicensis have been recorded as giving birth to two or three young, 

 and those that we have examined contained three and four embryos each. 



Habits. U. jamaicensis appears to be confined to shoal water, most frequently 

 (perhaps exclusively) on sandy or muddy bottom, most of the recorded captures of it 

 having been made in harbors or bays, where it is often taken in seines along shore as 

 well as in baited traps and on hook and line. Its method of securing its prey, not yet 

 observed, may resemble that of the closely allied U. halleri of the Pacific Coast (southern 

 California to Panama), which is "found on the bottom, nearly buried in loose sand or 

 mud," and which is "said to scoop out large holes in mad banks by waving the pectoral 

 fins, eating the worms, crabs, and small fishes thus exposed."!"' xhe only specimens for 

 which the stomach contents have been recorded contained shrimps [Penaeus hrasiliensis) 

 in one case, bottom detritus in another. 



A large male taken in Haitian waters was in breeding condition in March. 



Numerical Abundance. No precise information is available as to the numbers of 

 U. jamaicensis for any part of its range. Although it is plentiful enough for fishermen to 

 dread it in Jamaican waters, at most it has been reported as common at West Indian 

 localities, suggesting that it is not as abundant on the whole as its relative U. halleri is 

 along the Pacific Coast of Central America. Our observations around Bimini, Bahamas, 

 have indicated that it is seen or captured only occasionally there. 



103. One of this sex, with disc 190 mm long, has been described previously as in breeding condition (Beebe and Tee- 

 Van, Zoologica N. Y., 10, 1928: 30). 



104. Fowler, Monogr. Acad. nat. Sci. Philad., 7, 1945: 265. 



105. The presence of this structure was recorded by Garman (Proc. U.S. nat. Mus., 8, 1885: 41). 



106. Ann. Mus. Hist. nat. Paris, 4, 1804: 201, 210, pi. 55, fig. 2. 



107. Beebe and Tee-Van, Zoologica N. Y., 26, 1941: 269. 



