418 THE PLAGIOSTOMIA. 



of tail strong, depressed, with lateral folds, length from pores to spine three 

 fifths of that of the body from the pores forward. Tail sharply compressed 

 above the vertebrae behind the spine, with cutaneous folds above and below. 

 Back and tail rough with small, loosely-placed, stellate-based spines, larger on 

 the middle of the disk. Broad based, compressed and hooked-cusped tubercles 

 occur in irregular series above the vertebrae and along the lateral keels on the 

 base of the tail, similar tubercles arc irregularly placed along the middle of each 

 pectoral about half way from the base to the outer margin. 



Back brownish with scattered small spots of white; whitish below with 

 brown margins and with a few scattered spots of brown over the middle. In a 

 sketch of a young specimen in fresh condition the colors are yellowish to reddish 

 brown, closely freckled with rusty spots of darker and there is a yellow margin 

 on each pectoral. 



Length of disk 16, width 15, and length of tail from abdominal pores to 

 caudal spine 8 inches. 



Obidos, Brazil. Thayer Expedition. 



POTAMOTRYGON SCOBINA, sp. nOV. 



Disk round, tip of snout a slight prominence. Mouth small, in width one 

 third of its distance from the end of the snout, gently waved, with five papillae. 

 The papillae are arranged in two series : — the anterior containing a bifid median 

 papilla and one at each angle of the mouth; and the posterior two papillae 

 farther back than the anterior. Teeth small subequal, in H rows; crowns 

 transversely concave, rather smooth. Eyes small, lids curved outward on the 

 edge. Spiracles little larger than the eyes greatest distance apart contained 

 one and one half times in the length from snout to eyes. Disk and upper surface 

 of tail covered by very small fine closely set stellate-based spines intermixed 

 with larger above body and gills behind the head and in an area along the middle 

 of the upper side of the tail. Behind the middle of the abdomen above the 

 vertebrae there are two irregular rows of low, hooked broad-based tubercles 

 extending backward upon the base of the tail. Lower surfaces smooth. 



Back rusty brown with scattered small spots of whitish; ventral surfaces 

 brownish with small spots of white and with blotches of brown. 



Type an immature male from Cameta, Brazil. Length of disk 9| and 

 greatest width 9| inches. Thayer Expedition. 



