412 Memoir Sears Foundation for Marine Research 



The Peruvian G. afuerae Hildebrand 1946,*^^ which resembles G. micrura in hav- 

 ing no tail spines or spiracular tentacles, differs from micrura in its smaller eyes relative 

 to the spiracles, in the somewhat more acute anterior contour of its disc, and in the 

 absence of a longitudinal keel on the lower side of its tail. But the relationship remains 

 to be established between G. micrura of the Atlantic and the short-tailed spineless 

 Butterfly Rays without spiracular tentacles that have been reported as micrura from 

 South Africa,"* Borneo,'*' and Australia, ^^ ^s australis^^ from Australia, and as crooki 

 from Japan.*" See page 398 for comparison with other Atlantic species. 



Si-ze. The breadth of the disc at birth may be as small as six inches" or as great 

 as 8—9 inches. *2 Females produce young when 25—26 inches wide,*^ and probably 

 while smaller still, for a male only 420 mm wide (about 161/2 in.) in our Study Material 

 appears to have been nearing maturity, to judge from its claspers. A female 34 inches 

 wide from Chesapeake Bay, measured by us, was not only the largest among many but 

 was one of the largest ever reported that can be referred with confidence to the present 

 species rather than to G. altavela.^^ Thus it seems that the maximum breadth to which 

 this species ordinarily grows is not more than 3—4 feet. It is true that G. micrura has 

 been credited repeatedly with attaining a breadth of 6—7 feet, but all reports of Butterfly 

 Rays broader than 4— 4 1/2 feet from the western North Atlantic, under whatever name, 

 seem to have referred to G. altavela rather than G. micrura^ unless G. hirundo is a valid 

 species and occurs occasionally on the coast of North America. 



Developmental Stages. For an account of the developmental stages which un- 

 doubtedly apply equally to G. micrura and G. altavela^ see p. 397 under the genus 

 Gymnura. 



Habits. The Lesser Butterfly Ray appears to prefer a sandy bottom, so much so 

 that it is known locally in Chesapeake Bay as "Sand Skate." In the few recorded cases 

 from Beaufort, North Carolina and the vicinity of Woods Hole, Massachusetts, its 

 stomach has contained fragments of fish, crabs, shrimps, various bivalve mollusks (the 

 razor clam Solenomya among them), and even such minute objects as copepods, and the 

 megalops larvae of crabs. It is encountered most often in shallow water, as is illustrated 

 in Chesapeake Bay by the frequency with which it finds its way into the pound nets. 



55. Bull U.S. nat. Mus., 189, 1946: 71, 72, fig. 16. 56. Barnard, Ann. S. Afr. Mus., 21 (i), 1925: 80. 



57. Vinciguerra, Ann. Mus. Stor. nat. Genoa, ^o, 1926: 625. 



58. Fowler, Bull. U.S. nat. Mus., 100 (73), 1941: 457. 



59. Ramsay and Ogilby, Proc. Linn. Soc. N. S. W., 10, 1886: 575; Whitley, Fish. Aust., i, 1940: 208. 



60. Fowler, Proc. Acad. nat. Sci. Philad., 85, 1933: 241, fig. 6; Bull. U. S. nat. Mus., 100 {13), 1941: 455, 456, fig- 12- 



61. Smith, N. C. geol. econ. Surv., 2, 1907: 45. 



62. Our Study Material includes three embryos from South Carolina, 185-200 mm wide, about ready for birth, with 

 swollen abdomens but with the umbilical scar wholly obliterated; their identity as G. micrura is established by their 

 lack of spiracular tentacles or tail spines. 



63. Gudger, Proc. biol. Soc. Wash., 26, 1913: 100, as Pteroplatea maclura; RadclifFe, Bull. U. S. Bur. Fish., 34, 1916: 

 277- 



64. A Butterfly Ray 52 inches wide (1,320 mm) has been reported as G. micrura from Virginia (Fowler, Occ. Pap. 

 Mus. Zool. Univ. Mich., 56, 1918: 16), but without mention of the larger-growing G. alla'vela. While a New York 

 specimen, doubtless G. micrura because it was described as having no spiracular tentacles, was credited with a 

 breadth of two meters by Dumeril (Hist. Nat. Poiss., i, 1865: 615, as Pteroplatea maclura); this seems to have been 

 an error, since the same specimen had earlier been termed small by Muller and Henle (Plagiost., 1S41: 170). 



