420 THE PLAGIOSTOMIA. 



Teeth small, nearly equal, in if rows, crowns flattened, broad, inner edge rounded 

 and with a median and one or more lateral small sharp cusps. Eyes small, 

 prominent, distance apart less than two fifths of the distance from the tip of 

 the snout, lids curved outward. Spiracles more than twice as large as the eyes, 

 greatest distance apart less than length of snout. Body and head deep as com- 

 pared with the other species. Scales of the top of the disk sharp, stellate-based, 

 loosely set, larger over the middle of the body, absent near the margins. Very 

 irregular, closely set, broad-based, tubercles with tall hooked cusps occupy the 

 entire top of the tail between the lateral folds, and extend forward above the 

 abdomen and backward behind the caudal spine. Base of tail nearly half as 

 long as the body. 



Back brown, with indefinitely outlined spots of blue or greyish, larger than 

 the spiracles, separated by wide spaces. Ventral surface white in the middle 

 with scattered spots of brown; fins broadly margined with brown marbled 

 with white; inside of mouth and throat brown with white motthngs. Tail 

 brown or black, with spots of white below the base and in transverse bands 

 behind the spine. 



Length of disk II5, greatest width IO2, snout to abdominal pores 10?, 

 pores to base of caudal spine 5l inches. 



Type ( 9 ) from Montalegre, Brazil, on the Lower Amazon. 



POTAMOTRYGON SIGNATUS, Sp. UOV. 

 fTrygon hystrix Schomburgk, 1843, Fishes Guiana, 2, p. 180 (part), pi. 20 (smooth figure only). 



Disk subelliptical, a httle longer than wide, with regular curvatures, the 

 shape behind the middle closely resembfing that in the forward half. Eyes 

 much smaller than the spiracles, prominent. Mouth small, curved, width two 

 fifths of the distance from the end of the snout, one half of the interspiracular 

 distance and one third of the distance from the eye to the end of the snout, 

 with five papillae at the bottom. Anterior nasal valves confluent, reaching the 

 mouth, median attachment narrow. Teeth small, flattened on the crown with 

 a sharp angle directed inward, in li (to Is) rows, outer chestnut colored or 

 rusty, inner white. Entire upper surface of body covered with small stellate- 

 based sharp-cusped spines, larger on the middle of the body and along the 

 vertebral column. Top of tail with like protection besides a median dorsal 

 series of (about eighteen) broad-based tubercles with high sharp compressed 

 hooked points. Sides of tail naked. Base of tail, from pores to spine, four 



