1895.] FRILLED LIZARD OF TROPICAL AUSTRALIA. 713 



This takes the form of a voluminous denticulated frill, which the 

 creature possesses the power of erecting and depressing at will. 

 In adult individuals, the frill, when fully extended, may measure 

 as much as eight or nine inches in diameter, and diverges at 

 right angles to the long axis of the head. When depressed the 

 structure is relatively inconspicuous, being folded in symmetrical 

 pleats around the creature's neck (see fig. 2, p. 717). 



The possession of living examples of Chlamydosaurus, both iu 

 Queensland and, more recently, in Western Australia, has yielded 

 me the opportunity of observing and placing on record certain 

 phenomena associated with its habits that are scarcely less 

 remarkable than its structural peculiarities. Having, moreover, 

 succeeded in bringing one of these singular Lizards alive to 

 England, I had much pleasure in presenting the specimen to 

 this Society's Gardens, where others specially interested in this 

 animal group have been afforded opportunities of verifying the 

 observations embodied in this communication. 



In the first place, with reference to the elevation and depression 

 of the membranous frill, Chlamydosaurus is not unfrequently 

 delineated in natural-history vrorks with tliis structure more or 

 less fully extended, but with the mouth completely closed. I 

 have also observed mounted specimens in museums displaying a 

 corresponding relationship of the organ and structure indicated. 

 As a matter of fact, the opening of the mouth and the erection 

 of the frill are synchronous actions which cannot be exercised 

 independently of one another. An explanation of this circum- 

 stance is afforded by the presence of slender processes of the 

 hyoid bone which extend on either side through the walls of the 

 membranous frill. The relative elevation of the frill is consequently 

 in a direct proportion with the depression of the mandible, and it 

 is only under the condition of the mouth being opened to its widest 

 extent that the frill is so conspicuously displayed as to stand out 

 at a right angle from the animal's neck, as illustrated in the 

 drawing now exhibited (Plate XLI.) 



With regard to the significance and utility of the erectile frill in 

 Chlamydosaurus, the fact that this structure is of insignificant 

 proportions in young examples, and attains its full development 

 only in adult individuals, would appear to indicate that, as a 

 structure, it has been developed within comparatively recent 

 times and does not represent the residual heritage of a remote 

 ancestry. Bespecting its function, there can, I think, be but httle 

 doubt that it fulfils simply the role of a " scare-organ," where\\ath, 

 being suddenly erected, it terrifies, and diverts the projected attack 

 of, many ordinary enemies. The erection of the feathers of an 

 owl or the fur of a cat is associated with a like function, but the 

 inflation of the hood of the Cobra, and in a less degree the neck- 

 membranes of other snakes, furnishes, perhaps, a more appropriate 

 analogy. In one other Australian species, Amphiholurus harhatus, 

 commonly known as the Jew Lizard, the throat membrane is also 

 inflated under the influence of irritation in such a manner as to 



