460 Memoir Sears Foundation for Marine Research 



they have been heard to emit a loud harsh sound while struggling in a net.'^ But it is not 

 known whether they produce sounds of any sort under normal conditions. 



They feed chiefly on bivalve mollusks, such as clams and oysters, which they crack 

 with their dental plates. And they separate out the shells so expertly, probably by means 

 of their buccal papillae (p. 457), that the stomach contents of many specimens from the 

 North Carolina Coast and from the Tortugas consisted solely of the bodies of clams, 

 often practically intact, without any fragments of shell. 



So severe are their depredations, that an eyewitness writes of clam beds on the 

 coast of North Carolina entirely destroyed by them in less than a week;'^ and they are 

 said to be even more destructive to the pearl oyster beds of Ceylon. 8" 



Around Ceylon, however, fragments of fish, of gephyrean worms, of prawns, and of 

 octopus have been found in their stomachs," evidence that their diet is not as exclusively 

 molluscan everywhere as it is off the United States Coast. It is recorded also that the 

 stomach of one five feet wide, taken in Ceylon waters, contained seaweed. ^^ 



The suggestion «3 that they use the projecting lower dental plate like a spade to 

 dig out shellfish, etc. from sandy bottoms appears to be correct; the subrostral fin 

 perhaps serves as an aid, and the water is kept cloudy with the sand that is disturbed 

 as they feed along the shallows at high tide. 



Spotted Duck-billed Rays are seldom encountered more than a mile or two from 

 land, if that far, though their presence around Bermuda and among the various island 

 groups of the tropical-subtropical Pacific proves that they are capable of extensive 

 journeys across the open sea; there are many published records of their being taken in 

 seines along the beach «* and of their occurrence in more or less enclosed situations. But 

 they appear to enter estuarine situations much less freely than do the Butterfly Rays 

 (pp. 396, 413) or some of the more plentiful dasyatids (pp. 337, 375), for recent reports 

 of their presence in the partially enclosed waters near Beaufort, North Carolina, have 

 been based mainly on odd individuals, although they occur in large numbers in some 

 years along the open coast in the vicinity of Cape Lookout nearby.*^ There is nothing 

 in the published records of their occurrences along tropical West Africa to suggest that 

 they enter the multiple mouths of the Senegal River, «« though various other Rays do 

 so, commonly. 



It is probable that the Spotted Duck-billed Ray is a year-round resident through- 



78. Coles, Bull. Amer. Mus. nat. Hist., 32, 1913: 30. 79. Coles, Bull. Amer. Mus. nat. Hist., 28, 1910: 338. 



80. Norman and Fraser, Giant Fishes, 1937: 78. 



81. Pearson, Ceylon Adm. Rep. Mar. Biol., 1912-1913: E. 5. 



82. Thurston, Bull. Madras Govt. Mus., i, 1S94: 45. 83. Owen, Odontogr., 1840-1845: 47. 



84. Its close relative, Aetobatus fiagellum, has been described as frequenting the surf along the Senegal Coast (Roche- 

 brune, Act. Soc. linn. Bordeaux, [4] 6, 1882: 56). 



85. Characterized many years ago as "very common" (Yarrow, Proc. Acad. nat. Sci. Philad., 29, 1877: 216) near 

 Beaufort, North Carolina, but without information as to whether the reference was to the enclosed waters inside 

 the barrier beaches or to the open coast outside. 



86. A. narinari has been listed as occurring in fresh water (Smith, Biol. Rev. [Cambridge], 11, 1937: 65; Gunter, Amer. 

 Midi. Nat., 26, 1941 : 196). However, the record on which this statement was based was of one from a Siamese lagoon 

 connected with the open sea where the salinity was extremely variable, hence there is no proof that the specimen 

 actually was taken from fresh water (Hora, Mem. Asiat. Soc. Beng., 6, 1924: 465). 



