406 THE PLAGIOSTOMIA. 



angle of ventrals acute, anterior rays three or four times as long as the posterior. 

 Tail strong, tapering to a slender point, depressed anteriorly, longer than the 

 disk including the ventrals; caudal spine inserted in the end of the anterior half; 

 caudal fins not deep, origin of supracaudal at end of spine -of subcaudal farther 

 forward. Skin smooth, excepting above the vertebrae from above the pelvis, 

 on the back to the caudal spine where there is a series of broad-based compressed 

 and depressed backward directed sharp tubercles, 1-9, absent on young. Eyes 

 small, less than half as long as the spiracle, length less than one fourth (if their 

 distance apart. Mouth small, nearly one third the length of the snout, arched 

 forward, a median papilla at the bottom. Teeth in || rows. Total length 15, 

 tail from pores 8, and width 7| inches. 



Of a large number of specimens no two are alike in number and positions of 

 the tubercles, and in all cases they are supracaudal, between pelvis and caudal 

 spine. 



Hardly to be separated from U. chilcnsis Giinther, 1871. 



Panama. Hassler and John E. Thayer Expeditions, numerous examples. 



Urotrygon mtjndtjs. 

 Plate 30, fig. 1-2. 



Urotrygon mundus Gill, 1863, Proc. Acad. nat. sci. Phil., p. 173. 



Urolophus asterias Jordan & Gilbert, 18S2, Proc. U. S. nat. mus., 5, p. 579; Jord. & Everm., 1896, 



Bull. 47, U. S. nat. mus., p. 82. 

 Urolophus rogersi Jordan & Starks, 1S95, Proc. Cal. Acad, sci., scr. 2, 5, p. 388. 



Disk nearly round, little longer than wide if the ventrals are included, snout 

 slightly produced. Tail strong and depressed anteriorly, slender backward, 

 with spine inserted about mid length. Eyes small, length of orbits two and one 

 half times in their distance apart, nearly six times in the length of the snout. 

 Spiracles larger than the eyes. Mouth small, width two and one half times in 

 its distance from the end of the snout. Velum at the bottom deeply fringed. 

 In an eight inch male, fully mature, the teeth are in |g rows and have long sharp 

 cusps. Nostrils small, anterior valves short, with narrow median attachment 

 in front of the mouth. Shoulder girdle in the posterior half of the disk including 

 the ventrals. Pelvis arched forward in the middle. Ventrals broad, short, 

 outer angles blunt, claspers short, stout, crooked. Caudal narrow, pointed, 

 like that of U. chilensis. Spines small to very small, stellate-based, sprinkled 

 somewhat losely over the entire disk, rather more thickly in front of the head 



