Fishes of the Western North Atlantic 443 



the western Atlantic and M. aquila of the eastern Atlantic are the greater size of the 

 dorsal fin of the former" and its position farther forward on the tail (see Key, p. 438). 

 A longer and more narrowly ovate subrostral lobe may also prove to be a diagnostic 

 character for M. freminvillii as contrasted with M. aquila (Fig. 102), though accounts of 

 the latter differ widely in this respect. Also, the single large conical tubercle that develops 

 on the inner anterior rim of each orbit in mature males appears to be less prominent in 

 M. aquila than in M. freminvillii^ or it may even be absent. ^s 



Size. The usual breadth at birth is probably about 250 mm, for embryos about 

 200 mm wide have been born prematurely when their mothers were captured.^* Males 

 may mature at a breadth no greater than about 600—700 mm.^" The largest specimens 

 of which we find definite record are: one 34 inches wide from Chesapeake Bay," and 

 a female of about the same size (860 mm wide) trom Woods Hole, Massachusetts (see 

 Study Material). 



Developmental Stages. This is one of the Rays in which the uterus is known to be 

 lined with villi. Gravid females, taken near Cape Lookout, North Carolina, have been 

 reported as containing six embryos folded together in pairs, the heads and tails of each 

 pair in reversed position. ^^ 



Habits. The stomachs of specimens taken near Woods Hole, Massachusetts, con- 

 tained lobsters chiefly, also crabs (Cancer), clams (Mya), and large gastropods {Lunatia). 

 Presumably it feeds similarly on the larger Crustacea and on hard-shelled mollusks 

 throughout its range elsewhere. Nothing else is known of its method of life beyond 

 what applies to the genus as a whole (p. 436). In the northern part of its range it is 

 known as a summer and early autumn visitor only. In the years when it is most plentiful 

 it appears to arrive about as early and to linger as late near its extreme northern boundary 

 as it does along the middle Atlantic states; the earliest and latest reports of it are for 

 June and October both off southern Massachusetts and in Chesapeake Bay. No definite 

 information is available as to its seasonal occurrence anywhere to the southward. But 

 sea temperatures suggest that it may be expected off North Carolina from May through 

 November and in Brazilian waters the year round. It is probably a year-round inhabitant 

 also in the West Indian and Caribbean regions, if it occurs there with any regularity, 

 which is not yet known. 



Numerical Abundance. This Eagle Ray has never been reported as abundant any- 

 where, except by its original describer, and subsequent information makes it highly 

 probable that his characterization of it as "very common"^^ in the small inlets on the 

 Rhode Island Coast, where he "had an opportunity of examining many fresh specimens 



27. Base of dorsal fin only about 70 "/„ as long as distance between inner ends of exposed nostrils in M. aquila, but about 

 as long as distance between nostrils in M.fremin'villii. 



28. See page 437 for comparison with eastern Pacific species. 



29. Gudger (Proc. biol. Soc. Wash., 26, 1913: loi). The two smallest specimens in our Study Material, 140 and 144 mm 

 wide, are embryos and two others, 170 and 183 mm, seem to be also. 



30. The claspers of males 603, 710 and 760 mm long, in our Study Material, appear to be fully developed. 



31. Hildebrand and Schroeder, Bull. U.S. Bur. Fish., 43, 1928: 69. 



32. Gudger, Proc. biol. Soc. Wash., 26, 1913: loi; Coles, Proc. biol. Soc. Wash., 28, 1915: 94. 



33. Lesueur, J.Acad, nat. Sci. Philad., 4, 1824: 113. 



