454- lloyal Society, 



adjacent to the apex, are found to have lost the outer and the middle 

 layers, the innermost alone remaining. In the Auricula, this inner 

 layer also is removed, leaving a simple cavity in the upper half of the 

 shell. The absorption of the substance of these internal portions of 

 shell gives more space for the body, at the same time that it renders 

 the shell much lighter, without any diminution of its strength j the 

 body being sufficiently protected by the outer whorl. In the Murices, 

 and other shells having ridges or spines on the front of the whorls, 

 which, in the progress of the growth of the shell, the succeeding 

 whorls would necessarily overlap, t ? ese appendages are generally ab- 

 sorbed, to make way for the succeeding whorls ; their absorption 

 being effected by the edge of the mantle as it comes in contact with 

 them. Thus do many species of Mollusca absorb, at regular epochs 

 of their growth, certain parts of their shells, which had, at a preceding 

 period, been deposited about the lip in the form of ribs or teeth. 

 Mollusca have also the power of forming excavations in the shells of 

 other animals of this class, and sometimes of other individuals of the 

 same species : many instances of these facts are adduced by the au- 

 thor ; among which one of the most curious is the history of the Spi- 

 raglyphus, which, in the progress of its enlargement, absorbs a tubu- 

 lar portion of shell which it had formed at an early period of its growth. 

 They also excavate portions of solid rock in providing for their habi- 

 tation. Molluscous animals, however, do not appear to be capable 

 of removing extraneous obstacles which oppose their progress in the 

 formation of their shell j in proof of which, various examples are ad- 

 duced of foreign bodies being inclosed in the layers of shells. The 

 author produces evidence of the secretion of the materials of the shell 

 by other parts than the mantle, and in particular by the upper part 

 of the foot. The operculum is in this way formed, in a manner exactly 

 similar to shell, by the back of the foot : and its various modifications 

 of form, the author remarks, afford important characters for the sy- 

 stematic classification of this department of Natural History. 



June 20. —Professor Stromeyer, Foreign Memb. R.S., presented two 

 specimens, one of the coarse-grained, the other of the fine-grained va- 

 riety, of the remarkable mass of iron lately discovered near Magdeburg, 

 and an account of which had been laid before the Royal Society of Got- 

 tingen on the 14th of last month. This iron was found, in several de- 

 tached lumps, about four feet below the mould, by Mr. Kote, who 

 considered himself the more authorized to pronounce it meteoric, as, 

 in the chronicles of Magdeburg, the descent of a fiery meteor is re- 

 corded as having happened in the year 998*. Professor Stromeyer has 

 subjected this iron to a minute analysis, the results of which are very 

 interesting, inasmuch as, besides the alloy of nickel and cobalt, usu- 

 ally present in meteoric iron, he unexpectedly found a considerable 

 portion of molybdenum, — a rare metal on our planet, occurring only 

 in two combinations, viz. with sulphur, as glance molybdenum, and, 

 as molybdic acid combined with oxide of lead, in the yellow lead 

 ore of Carinthia and a few other places. 



• The information extant on this subject would appear to be more pre- 

 cise than is here indicated ; for Chladni has recorded the actual fall of me- 

 teorites at Magdeburg, in the above year. See Phil. Mag. vol. lxvii. p. 5. — Ei>. 



