There are a 5 species of large round stingrays, which are all known locally as bull rays. They are all dark with a light underside. If the tail is used as an identifier, remember that parts can be broken off.

Black-spotted Stingray Taeniura meyeni (Syn.Taeniura melanospila) Muller & Henle 1841
Grey with black spots, or black and white mottled, no thorns, white margin, deep skinfold to tip of tail. Bottom feeder, eats crustaceans and molluscs. (pictured above)

Stingrays have barbed and venomous spines. the curved spine pictured below is 18cms long could be that of a black stingray, Dasyatis thetidis. The small points on the side are very sharp and curve backwards, once embedded they are difficult to remove.

Black Stingray, thorntail ray  Dasyatis thetidis Ogilby 1899
The black stingray is found near beaches, in coastal waters and to depths of 300m. It is about 1.8m wide, similar in appearance to the Smooth Stingray, but differs in that it has short tubercles on top of the head, in the middle of the back and on the tail. The tail is longer than the disc width. These stingray have single, serrated and venomous barbs which were once prized as letter openers.
Naming notes:-
dasys means rough or dense,
atus means shark,
thetidis means of the sea

Smooth Stingray  Dasyatis brevicaudata Hutton 1875
The smooth stingray is the largest stingray, being up to 2.1mwide. It has no thorns on the head or back but does have a row of white pores on either side of the head. The tail is shorter than the disc width. Habitat ranges from estuaries to 170m depth. Smooth Stingrays eat bony fish, bivalves, squid and crustaceans.
Naming notes:-
dasys means rough or dense,
atus means shark,
brevi means short,
caudata refers to the tail.

Estuary Stingray, brown stingray  Dasyatis fluviorum Ogilby 1908
The estuary stingray, is a smaller ray growing to a maximum width of 1.2m. It has a very long tail, with no skinfold. There are enlarged denticles along the midline and tail. This ray eats shellfish, including farmed oysters.
Naming notes:-
dasys means rough or dense,
atus means shark,
fluvius latin for river

Cowtail Stingray, banana tail ray  Pastinachus sephen Forskkal 1775
The Cowtail Stingray can reach 1.8m across but it is usually smaller in Australian waters. It is named for the deep fin like skin fold below its very long tail. It is found in inshore locations. In WA they have been seen resting in the sun in very shallow water and can be found in large congregations. They can be found on sandy bottoms and also among mangroves. They dig up molluscs and crustaceans by flapping up and down to create suction. Like many stingrays, they carry dangerous tail spines. The skin was used in Sumatra for drum skins and in Japan for binding sword hilts.