Fishes of the Western North Atlantic 375 



Atlantic. But it appears clearly separable from D. pastinaca by: a much longer tail 

 (not much longer than disc in pastinaca), a relatively longer snout, its more deeply 

 concave nasal curtain, its much more broadly rounded outer pectoral corners, and its 

 somewhat more highly developed upper tailfold. D. pastinaca also grows to a consider- 

 ably larger size at maturity. In general form, D. sabina resembles the West African 

 D. Margarita, but the upper surface of the tail of the latter lacks a fold, while the 

 armature of its disc, with a single large round tubercle in the middle of the back sur- 

 rounded by numerous small tubercles,"^ is different. 



Size. This is the smallest of the long-tailed Sting Rays of the western Atlantic. 

 Embryos ready for birth are reported as having discs about 100 mm wide; gravid 

 females have been described as not much larger than newborn D. centroura, i. e., with 

 discs only 160—176 mm wide; a female about 10 inches wide has been reported as 

 having the tail of an embryo protruding from her cloaca and a male of about that same 

 size has been reported as being fully developed. The largest we have seen are a female 

 390 mm wide and a male of 270 mm in which the claspers apparently are fully formed 

 (Fig. 88). Three specimens with discs 458-610 mm long appear to be the largest 

 recorded."* 



Developmental Stages. The smallest embryos seen, with discs about 35—36 mm 

 wide, were already of the same shape as their parents, but no information is available 

 as to the stage in development at which the tailfolds become apparent. Females have 

 been found to contain one to three embryos, the males slightly outnumbering the 

 females on an average {^c^d %), though one litter, three in number, has been reported as 

 consisting of females only.^^^ 



Habits. This little Sting Ray is encountered most commonly close to the shore 

 line in bays and sounds in depths no greater than seven to eight feet. We find no 

 definite report of it even off open coasts at depths greater than the maximum fished by 

 the shrimp trawlers of Louisiana, about 70 feet. 



Observations on the Texas Coast (p. 376) suggest that it tends to avoid tem- 

 peratures lower than about 16° C (61° F), though it has been taken in water as cold 

 as 13.7° C (56—57° F). It has been recorded in water as warm as 30.5° C (87° F),"* 

 and to judge from its geographic distribution, it probably finds nothing detrimental 

 in even somewhat warmer situations. 



The salinity of the water influences its distribution but little if at all, for it occurs 

 throughout the entire range from fresh water up to full oceanic salinity (upwards of 

 36 "/oo)- However, in Texas waters it has been found to be least common where the 

 water is less saline than 10 '/oo ^.nd most common in salinities higher than 30 "/oo;^*' 

 this makes it doubtful whether Z). sabina can exist permanently in water that is not at 

 least slightly brackish. 



113. For a recent description and illustrations of D. margarita, see Fowler (Bull. Amer. Mus. nat. Hist., 70 [i], 1936: 

 127). 



114. Fowler, Proc. Acad. nat. Sci. Philad., 7S, 1926: 249. 



115. Breder and Krumholz, Zoologica N. Y., 26, 1941: 49. 



116. Gunter, Publ. Inst. mar. Sci. Texas, /, 1945: 22. 117. Gunter, Publ. Inst. mar. Sci. Texas, J, 1945: 22. 



