[Garman. 210 [May 2. 



Potamotrygon gen. nov. 



Disk oval, lengthening with age. Head rising little above the 

 level of the body. No prominence on the side of the spiracle. Taie 

 depressed anteriorly; posteriorly compressed into a sharp anglle 

 above, and, becoming calcined, easily broken. Peripheral vascular 

 system not forming a network on the ventral surface. Oral papillaB 

 prominent. With asperities and tubercles. 

 Species that cannot be determined : 

 Aiereba Marcgrave, Pise. Bras., 1648, p. 175. 

 " Jonston, De Pise, 1649, Tab. 38, f. 6. 

 " Willoughby, Hist. Pise, 1686., p. 68, Tab. C 1, f. 2. 

 Raja orbicularis Bl. Schn. Syst. Ichth., 1801, p. 361. 

 Trygon aiereba Mull, et Henle, Plagiost., 1841, p. 160 (not 196). 

 The specimens at hand furnish characters sufficient for the estab- 

 lishment of the species indicated by the following synopsis. 



Body longer than wide, thick, marked with irregular lines of dark 

 brown, which often form networks of polygons, or rounded spots, 



sometimes uniform. Teeth small Humboldtii. 



Body nearly round, moderate, commonly marked with round 

 spots of yellow or orange with dark brown borders, varying in color 

 from light yellowish with numerous spots to uniform dark brown. 



Teeth larger . . , . motoro. 



Body nearly round, thin, marked above with brown lines or spots 

 often uniform light brown. Adult with blotches of brown below. 



Teeth very small Dumerilii. 



Potamotrygon Humboldtii. 



Pastinaca Humboldtii Roulin, Ann. Sc. Nat., 1829, xvi, p. 104, pi. 3. 

 Trygon hystrix Miiller & Henle, Plagiostomen, p. 167. 

 " " D'Orbigny, Voy. Amer. Merid., Poiss., pi. 15, 1847. 



" » Schomburgk, Fish. Brit. Guiana, p. 180, pi. 20, 1852. 



" " Castelnau, Anim. Amer. Sud, Poiss., p. 103, 1855. 



Trygon {Tcenura) OrbignyiC&st., 1. c, p. 102, pi. 49, f. 1. 



" hystrix Dumeril, Elasmobranchs, p. 608, 1865. 

 Tceniura Orbignyi Dum., 1. c, p. 624. 

 " Magdaleno3 Dum., 1. c, p. 625. 



" Orbignyi Giinther, Cat. Fish. Brit. Mus., viii, p. 484. 

 Trygon hystrix Giinth., 1. c., p. 482. 



Disk oval, rounded in front, longer than broad, narrower in the 

 posterior half. Body thicker than that of the other species. Head 



