The phrase "a third species of" is correct and usable in written English.
It can be used when discussing biological classifications or categories, particularly when introducing an additional type or variety within a group.
Example: "In addition to the two known species, researchers have identified a third species of frog that exhibits unique characteristics."
Alternatives: "an additional type of" or "a new category of".
Systematic Revision within the Phalanger orientalis complex (Diprotodontia, Phalangeridae): a third species of lowland gray cuscus from New Guinea & Australia.
And a third species of service lets people set up their own personalized gates to the Web, a la My Yahoo, but with the option of gathering headlines or bits of data from whatever sites the users choose.
In 1990, Faure and Guerin described a third species of Malagasy hippopotamus, Hippopotamus laloumena ("laloumena" is a Malagasy word for hippopotamus), which was a distinct species.
According to the BBC, the newly recognized species is unique because of its larger, flatter shell, and is related to a third species of land snail found on Japan's Ishigaki Island.
A third species of human type I interferon is known as IFN-ω [ 7].
A third species of Ebolavirus, Reston ebolavirus, was isolated from Cynomologus monkeys imported from the Philippines to a facility in the United States, where they experienced severe haemorrhaging (Jahrling et al., 1990).
A second species of Latimeria was discovered in Indonesia in 1998.
A second species of Coptotermes was collected in Mount Glorious, Queensland, Australia.
A little later, Frank Kingdon Ward discovered a second species of Beesia in Burma which was named Beesia deltophylla.
Dr. Sandra Shumway, a shellfish biologist at the University of Connecticut, after whom Dr. Burkholder named a second species of pfiesteria, denied that it was a usual practice in marine biology for scientists to share their strains after a first publication.
And best of all, a fifth species of tit: the crested, a bird we'd been hoping to see, as this is the only part of Britain where it can be found.
