XVII ELASMOBRANCHII BATOIDEI 465 



as well as on the adjacent coasts, and specimens have been 

 obtained from Lake Munroe at some distance from salt water.^ 

 Ellipesuriis and Paratrygon are freshwater genera, found in 

 Colombia, Venezuela, and Guiana. 



Fossil remains of undoubted Trygonidae appear to be confined 

 to the Tertiary period. 



Fam. 7. Myliobatidae (Eagle-Eays). — Disc much broader than 

 long, and rhombic in shape. The huge pectoral fins are not 

 continued to the extremity of the snout, but cease on the sides 

 of the head, and reappear in front of the snout as a pair of 

 distinct folds, the so-called cephalic fins. The head projects 

 above the level of the disc, and consequently the eyes and 

 spiracles are lateral in position. Tail long, slender, and whip- 

 like, with a single dorsal fin near the root, and usually one or two 

 serrated spines behind the fin. A rectangular naso-frontal fold is 

 present. The dentition consists of flat, hexagonal, pavement-like 

 crushing teeth arranged from before backward in arched rows in 

 both jaws, and there is either a single median row of large teeth, 

 with (e.g. Myliolatis) or without (e.g. Aetobatis) the addition of 

 several rows of much smaller teeth on each side, or there are 

 numerous rows, the teeth then decreasing in size from the middle 

 line laterally (e.g. Bhinoptera). Skin smooth. Sexes similar. 

 Five genera and about twenty -seven species are known; all 

 inhabitants of tropical and subtropical seas. 



Myliolatis is represented in the Mediterranean by two species, 

 and one of them, the almost cosmopolitan M. aquila (Fig. 266), 

 has been taken at various points on the eastern and southern 

 coasts of England. Aetoha.tis is also widely distributed in 

 tropical seas, but is unknown in European waters. Bhinoptera 

 has one species in the Mediterranean, while others have been 

 recorded from Brazil, the Atlantic and Pacific coasts of North 

 America, and the East Indies. The two tropical genera 

 Dicerohatis and Ceratoptera have the cephahc fins prolonged 

 anteriorly into a pair of horn-like appendages, which are said 

 to be used in conveying food to the mouth. The teeth are 

 small, flat or tubercular, and are arranged in numerous rows. In 

 Ceratoptera they are wanting in the upper jaw. The Eagle- 

 Eays feed principally on Molluscs, the shells of which they 

 crush with their large grinding-teeth. Some of them attain 



1 Jordan and Evermann, 0^;. cit. p. S-?. 

 VOL. VII 2 H 



