273 



l(nab) = -n((X') b cosT-f(Y') a sinT), 



b si 



cos I ty)= - ((X') b sin T + ( Y') a cos T) + 2a b sin T cos T -, 



in which ^- and -j- are the differential coefficients of the expressions 



for and r), taken explicitly with regard to t. 



This method is denominated the method of Osculating Variation. 



II. " Description of some Remains of a Gigantic Land-Lizard 

 (Megalania prisca, Ow.) from Australia." By Prof. 

 RICHARD OWEN, F.R.S. Received May 13, 1858. 



(Abstract.) 



The subject of this communication forms part of a collection of 

 fossil remains from Australia, recently acquired by the British Mu- 

 seum, and demonstrates the former existence in that continent of a 

 land-lizard considerably surpassing in bulk the largest species now 

 known. The characters are chiefly derived from vertebrae, partially 

 fossilized, equalling in size those of the largest existing Crocodiles ; 

 they are of the * proccelian ' type, but present lacertian modifica- 

 tions, and closely agree with those in the great existing * Lace-li- 

 zard ' of Australia (Hydrosaurus giganteus, Gray), of which indi- 

 viduals upwards of six feet long have been taken. A generic or sub- 

 generic distinction is indicated by the comparatively contracted area 

 of the neural canal, and by the inferior development of the neural 

 spine, of the fossil vertebrae, which have belonged to an indivi- 

 dual not less than twenty feet in length, calculated from the vertebrae 

 and proportions of the body of the existing Hydrosauri. For this, 

 probably extinct lizard, the name of Megalania prisca is proposed. 



The results of an extended series of comparisons of its vertebrae 

 with those of recent and extinct Sauria are given ; and the paper is 

 illustrated by drawings of the vertebrae of Megalania and those of 

 Hydrosaurus. 



