 The whip @-@ like tail generally measures up to one and half times the length of the disc , and bears one ( more if replacements have grown in ) long , slender , <unk> spine on the upper surface , closer to the base than the tip . Behind the spine , there are long dorsal and ventral fin folds that rise gradually , reaching a relatively high apex before sloping down abruptly . The presence of the upper fin fold separates this species from the similar <unk> stingray ( D. <unk> ) , which shares most of its range . However , the tail is often damaged , in which case <unk> the two species in the field becomes all but impossible . Young rays have completely smooth skin , while adults develop a row of low tubercles along the midline of the back , flanked by two shorter rows on the " shoulders " . The tail also becomes covered in <unk> . This species is a uniform olive to brown to gray above , darkening to black on the tail , and off @-@ white below . 
