The comb-bearing dragons of the genus Ctenophorus are an assemblage of 28 (and counting!) species of medium-sized lizards found around Australia. Darren Naish has recently been giving an overview of the Australian dragons; you can read what he's already said about Ctenophorus here. I'd suggest reading that first, then coming back here.
Species of Ctenophorus are distinguished from other dragons by the presence of a row of tectiform (roof-shaped) scales running from behind the nostrils under the eyes, though in some species this row is only weakly pronounced (Melville et al. 2008). In most species, the tympanum (ear-drum) is exposed, though a few species have it covered over. I'm personally familiar with one species of Ctenophorus, the ring-tailed dragon C. caudicinctus. Where we've been doing fieldwork on Barrow Island, ring-tailed dragons are a common site perched on termite mounds or larger rocks, invariably just one dragon to a rock, monitoring the surrounding territory for food or mates. Not all Ctenophorus species engage in such behaviour: the species have been divided between three groups depending on whether they prefer rocky habitats, whether they prefer sandy habitats and use tufts of spinifex and other vegetation for cover, or whether they shelter in burrows. Phylogenetic analysis suggests that the burrowing habit was ancestral for the genus; rock-dwelling or scrub-dwelling habits may have each evolved more than once within Ctenophorus, though the possibility cannot be entirely ruled out that they may characterise monophyletic groups (Melville et al. 2001). These differences in ecology also correlate with morphological differences: rock-dwelling species have dorsoventrally flattened heads, while the scrub-dwelling species are long-legged and cursorial.
While some species of Ctenophorus are widespread, others are far more restricted in range. Ctenophorus caudicinctus, for instance, is found across most of northern Western Australia and the Northern Territory, but Butler's dragon* C. butleri is restricted to coastal sand dunes between Shark Bay and Kalbarri in Western Australia (Cogger 2014). The most recently described species to date, the Barrier Range dragon C. mirrityana, is known from two locations about 100 km apart in western New South Wales (McLean et al. 2013). And it possibly does say something that new species continue to be described even in this not inconspicuous genus.
*Or should that be 'Butlers' dragon', as it was apparently named after both Harry and Margaret Butler?
Perhaps the most hard-core of the comb-bearing dragons is the Lake Eyre dragon Ctenophorus maculosus, a specialised inhabitant of dry salt lakes in South Australia. This is a spectacularly harsh environment: searing hot sun, often at temperatures above 40°, beating down on a crust of crystallised salt. Few other animals can survive there without spontaneously combusting. The dragons protect themselves from the head by burrowing into the layer of unconsolidated sand beneath the salt-crust; Pedler & Neilly (2010) discovered one female with its head protruding from a burrow with an entrance too small for its body, and suggested that she must have gotten there by 'swimming' through the sand. The Lake Eyre dragons feed on ants such as Melophorus (themselves no slouch in the hard-core stakes) or other insects that have become stranded on the salt-pan. When the lake becomes filled with water (as it does about once a decade or so), the dragons are forced to flee into the habitats surrounding the lake shores and wait for the flood to clear. Two Western Australian species, the claypan dragon Ctenophorus salinarum and the Lake Disappointment dragon C. nguyarna, are also associated with salt-pans, but they do not have quite the level of specialisation of the Lake Eyre dragon.
Cogger, H. G. 2014. Reptiles and Amphibians of Australia, 7th ed. CSIRO Publishing: Collingwood.
McLean, C. A., A. Moussalli, S. Sass & D. Stuart-Fox. 2013. Taxonomic assessment of the Ctenophorus decresii complex (Reptilia: Agamidae) reveals a new species of dragon lizard from western New South Wales. Records of the Australian Museum 65 (3): 51-63.
Melville, J., L. P. Shoo & P. Doughty. 2008. Phylogenetic relationships of the heath dragons (Rankinia adelaidensis and R. parviceps) from the south-western Australian biodiversity hotspot. Australian Journal of Zoology 56: 159–171.
Melville, J., J. A. Shulte II & A. Larson. 2001. A molecular phylogenetic study of ecological diversification in the Australian lizard genus Ctenophorus. Journal of Experimental Zoology 291: 339-353.
Pedler, R. & H. Neilly. 2010. A re-evaluation of the distribution and status of the Lake Eyre dragon (Ctenophorus maculosus): an endemic South Australian salt lake specialist. South Australian Naturalist 84 (1): 15-29.