Royal Society. 273 



mucus in its coats, and is thence impelled with considerable force 

 into the duodenum. The oesophagus is wide, admitting of lar<*e 

 masses of food being swallowed, and of regurgitation : the open- 

 ing of the pylorus is small and valvular, preventing the passage of 

 its contents back again into the duodenum : the structure of the 

 duodenum, pylorus, and adjacent organs, is very similar to that of 

 those of the Seal. It had been observed by Mr. Fisher, the astro- 

 nomer to the late expedition under Capt. Parry, that the food 

 of the Walrus is the Fucus digitatus, which is found in great 

 abundance in the Arctic seas, thrown up on the shores by the 

 waves, and also beneath the ice. 



The third fact to which Sir Everard Home adverts in this 

 communication relates to the structure of the funis and placenta 

 of the Seal, as observed in a specimen of those parts brought home 

 by Lieut. Griffiths, one of the officers in the late expedition under 

 Capt. Parry. The vessels composing the former are not twisted, 

 and are about nine inches long j at the distance of three inches 

 from the placenta, they anastomoze into blood-vessels, which are 

 connected with the placenta by three membranous coats; the 

 whole conformation giving great freedom to the embryonic circu- 

 lation. Drawings of this subject and that last noticed, made by 

 Mr. Rose, a pupil under the author at St. George's Hospital, 

 are annexed to the paper. 



March 25. — A letter to the President was read, from L. W. 

 Dillwyn, Esq. F.R.S., On the Geological Distribution of Fossil 

 Shells, in continuation of his former paper on that subject, pub- 

 lished in the Philosophical Transactions for 1823, and noticed in 

 the former number of this Journal, p. 120. 



The present communication contains further remarks on the 

 relative periods at which the various families of Testacea appear 

 to have been first created ; and suggests, that a regularly approx- 

 imating series may be observed, from the fossil remains of the 

 oldest formations, to the living inhabitants of our seas and rivers. 

 It is the author's opinion, that those Fossil Shells which cannot 

 be referred to any of the Natural Orders into which the living 

 Testacea have been divided, are only to be found in the beds 

 jbelow the Oolites ; and that in the Secondary beds above the 



