I o Memoir Sears Foundation for Marine Research 



the embryos of any of the batoids feed on unfertilized eggs that lie close to them in 

 the maternal oviduct, as do the embryos of Mackerel Sharks {Lamna) and of the Sand 

 Shark {Carcharias taurus) of the western North Atlantic.^! 



Luminescence. None of the batoid fishes have luminescent organs so far as is known. 



Habits and Food. Most of the batoids are comparatively sluggish, living on the 

 bottom or close to it. Even the Sawfishes (Pristidae) keep close to the bottom, except 

 when they may rise among a school of fishes ; although they are slow swimmers they 

 are strong, as any angler will testify who has hooked or harpooned one. The Guitar- 

 fishes (Rhinobatidae and Rhynchobatidae) either swim about slowly close to the bottom 

 or lie half buried. The Torpedoes (Torpedinoidea) lie buried in the mud or sand most 

 of the time and swim but feebly. The Skates (Rajidae) either lie flat on the bottom, 

 often with their pectorals partly buried, or swim along slowly close to it. But they can 

 dart ahead with astonishing velocity if disturbed or if in pursuit of prey (p. 143). The 

 Sting Rays and their kin (Dasyatidae, Urolophidae) have much this same way of life, 

 except that they are rather more likely to be wholly buried except for eyes and spiracles. 

 The Butterfly Rays (Gymnuridae) also hold close to the bottom, though perhaps 

 moving to and fro more actively with changes of the tide than most of the dasyatids 

 (p. 413). However, the Eagle (Myliobatidae) and Cow-nosed Rays (Rhinopteridae) 

 are decidedly more active, for while they feed right on the bottom (pp. 437, 466) they 

 often swim actively at midlevels or near the surface, sometimes leaping clear of the 

 water, as described elsewhere. The Devil Rays appear to have abandoned the bottom- 

 living habit largely and spend most of their time swimming close to the surface (p. 485). 



The batoids, like the Sharks, subsist wholly on animal food, and the lists of stomach 

 contents so far recorded are varied enough to show that practically all of the inverte- 

 brate groups characteristic of sandy or muddy bottoms contribute to the diet of one 

 or another Skate or Ray. The Eagle and Cow-nosed Rays as a group subsist chiefly 

 on hard-shelled mollusks, but they are known to take Crustacea on occasion (p. 473). 

 The dasyatid and Butterfly Rays (Dasyatidae, Gymnuridae) are rather more catholic 

 in their tastes, consuming small fish as well as Crustacea and mollusks. Skates (Rajidae) 

 as a group probably depend chiefly on whatever Crustacea may be available locally, 

 but they also devour mollusks, polychaete worms, and cephalopods of the less active 

 sorts, as well as small fishes, on which they may feed exclusively at times (p. 223). 



The Sawfishes (Pristidae) feed chiefly on fishes (p. 19) but to some extent on 

 bottom-living invertebrates as well. Some of the Electric Rays (Torpedinoidea) are 

 strictly fish-eaters, sometimes devouring fishes of considerable size relative to them- 

 selves, whereas others subsist on small bottom-living invertebrates. 



Most interesting of all are the feeding habits of the Devil Rays (Mobulidae). In 

 spite of the great size to which some of them grow, they feed on small Crustacea, small 

 fishes, and other members of the animal plankton which are directed by the fin-like 

 cephalic appendages into the mouth, there to be sifted out (from the water that is taken 

 in at the same time) by the so-called prebranchial apparatus, as is described on p. 483. 



21. Springer, Copeia, 1948: 154. 



