 The tail is slender and whip @-@ like , measuring approximately half as long as the disc . A stinging spine with strong serrations , measuring up to 35 cm ( 14 in ) long and equipped with a venom gland at its base , is positioned about a third of the distance along the tail . A second or even third spine may also be present , as the spines are regularly replaced and new spines grow in before existing ones have been shed . The tail behind the spine bears a low cutaneous fold on top and a short , deep fold underneath . The body and tail are smooth , save for a few dermal denticles on the leading edge of the disk ; older individuals may also develop a row of bony knobs along the midline of the back . This species is a solid gray , brown , reddish , or olive @-@ green above , and whitish below with dark fin margins . Young rays may have white spots . 
