66 Royal Society. 



8 or 10 inches in length ; and a tibia, found with the same, is 

 4 feet long. 



Dermal scutes and spines. — The author figures and describes se- 

 veral dermal scutes and spines, and states that a microscopical exa- 

 mination of the large angular bones of the Hylaeosaurus (Phil. Trans. 

 184'1, PI. X. fig. 1), supposed by him to be ossified dermal spines, 

 but which Professor Owen regarded as the abdominal extremities of 

 ribs, proves the correctness of his own opinion ; their structure being 

 identical with that of the acknowledged dermal scutes. 



In the summary which concludes the memoir, Dr. Mantell states 

 that the facts described, confirm in every important point the phy- 

 siological inferences relating to the structure and habits of the Igua- 

 nodon and Hylaeosaurus, enunciated in his former communications; 

 and thus, after the lapse of a quarter of a century, he concludes his 

 attempts to restore the skeletons of the colossal saurian herbivores, 

 of whose former existence a few water-worn teeth and fragments of 

 bones were the only indications, when, in 1825, he first had the ho- 

 nour to submit to the Royal Society a notice on the teeth of the 

 Iguanodon. 



March 15. — "Researches in Physical Geology." Part XL By 

 Henry Hennessy, Esq. Communicated by Major Beamish, F.R.S. 



In this communication the author states that, having in Part I. 

 (read to the Society in December 1846) endeavoured, by general- 

 izing the hypothesis on which is usually founded the theory of the 

 earth's figure, not only to improve that theory, but also to establish 

 a secure basis for researches into the changes which may have taken 

 place, within and at the surface of the earth, during the epochs of 

 its geological history, his object here is to discover relations between 

 the interior structure of the earth and phenomena observed at its 

 surface, and also the effects of the reaction of the fluid nucleus, de- 

 scribed in Part I., upon the solid crust. This memoir is divided 

 into sections, each containing a distinct investigation ; and the state- 

 ment of the geological results is given at the end. 



I. The Pressures of the Shell and Nucleus at their surface of contact. 



In the investigation of these pressures the earth is supposed to 

 consist of a nucleus of fluid matter inclosed in a solid shell, the inner 

 and outer surfaces of which are spheroidal, but nearly spherical ; 

 and both shell and nucleus are supposed to consist of strata varying 

 in density according to some unknown inverse law of the radii. The 

 pressure at the inner surface of the shell is conceived to be due to a 

 constant pressure, which is the same for every point, and a variable 

 pressure, arising from the difference in form of the surface of the 

 nucleus and inner surface of the shell. On these suppositions, simple 

 expressions for the pressure on any stratum of the nucleus and on 

 the shell's inner surface are deduced. 



II. The Variation of Gravity at the earth's surface. 



The author does not assume in this investigation that the laws of 

 arrangement of the particles composing the shell and the nucleus 



