Animal: Lidi (as opposed to the hairless Lidi which may or may not be a close cousin.)
Close Surface Cousin: diplodocus
At The Earth’s Core , Chapter 15 ; Pellucidar , Chapter 7
Environment: Lidi Plains
We had barely entered the great plain when we discovered two enormous animals approaching us from a great distance. So far were they that we could not distinguish what manner of beasts they might be, but as they came closer, I saw that they were enormous quadrupeds, eighty or a hundred feet long, with tiny heads perched at the top of very long necks. Their heads must have been quite forty feet from the ground. The beasts moved very slowly—that is their action was slow—but their strides covered such a great distance that in reality they traveled considerably faster than a man walks.
As they drew still nearer we discovered that upon the back of each sat a human being. Then Dian knew what they were, though she never before had seen one.
“They are lidis from the land of the Thorians,” she cried. “Thoria lies at the outer verge of the Land of Awful Shadow. The Thorians alone of all the races of Pellucidar ride the lidi, for nowhere else than beside the dark country are they found.”
Note: As opposed to the hariless lidi. These can be assumed to have hair and therefore are likely mammals.
Note: Wikipedia claims these are supposed to be diplodocus but the existence of the hairless-lidi mentioned in passing really does imply that is incorrect. Unless “hairless” is meant to describe the lidi instead of being a name. Burrough’s writing style and very fluid conventions on naming makes this a bit difficult to suss out. See dyryths versus sea dyryths or the fact that sea-dryths are also known as Tandors of the Sea (implying other types of tandors?). Additionally as the “hairless lidi” was used to explain what a mahar is, in the same breath as a thipdar we can assume something here is amiss: as thipdars are also hairless and diplodocus have little in common with mahars that they also don’t share with thipdars. Ergo the hairless lidi must have some commonality to mahars that diplodocus does not. Therefore we are assuming that “hairless lidi” and “llidi” are two creatures for the time being. The hairless variety may indeed match a 1920s conception of diplodocus.
Note: Burroughs likely is just being inconsistent and it’s showing; but we should err on the side of expanding the universe in more interesting ways imho.
Pellucidar , Chapter 7 removes all doubt
Lidi, by the way, is both the singular and plural form of the noun that describes the huge beasts of bur-den of the Thurians. They are enormous quadrupeds, eighty or a hundred feet long, with very small heads perched at the top of very long, slender necks. Their heads are quite forty feet from the ground. Their gait is slow and deliberate, but so enormous are their strides that, as a matter of fact, they cover the ground quite rapidly.
Perry has told me that they are almost identical with the fossilized remains of the diplodocus of the outer crust’s Jurassic age. I have to take his word for it—and I guess you will, unless you know more of such matters than I.