199 



apertures, are possessed of similar powers. In the other genera of 

 turbinated univalves, the aperture, instead of being notched, is entire, 

 and they have all been proved to be herbivorous. Every turbinated 

 univalve which Mr. Dillwyn has examined of the older beds, from the 

 transition limestone to the lias, belongs to these herbivorous genera, 

 and the family still inhabits our land and waters. On the contrary, 

 all the carnivorous genera abound in the strata above the chalk, but 

 are very rare in the secondary strata. In recent shells small holes 

 bored by the predaceous Trachelipoda are common ; and Mr. Dillwyn 

 has observed similar holes in fossils from the London clay, but never 

 in those of the older formations ; and he thinks that the whole family 

 of carnivorous Trachelipoda are very rare in all those strata where 

 the Ammonites and other Nautilidse abound. Ammonites, and the 

 other principal multilocular genera, appear to have become extinct in 

 northern latitudes when the chalk formation was completed : but a few 

 of the Nautilidse still inhabit the Southern Ocean. Mr. Dillwyn further 

 observes, that all the marine genera of the herbivorous Trachelipoda, 

 to which the fossil species belong, have an operculum, and that, the 

 carnivorous species of the secondary strata agree with them in this 

 particular, though the unoperculated genera abound in the London 

 clay. Although fossil Nautilidae are common in the secondary strata 

 of the United States, they are said not to have been found in South 

 America. Hence, says the author, it may be queried whether the 

 Cephalopoda were not confined to the more northern latitudes when 

 the chalk formation was completed ; and whether a decrease in the 

 earth's temperature at that period may not have occasioned the entire 

 destruction of some genera, and the migration of others to the south. 



On the apparent Magnetism of Metallic Titanium. By William Hyde 

 Wollaston, M.D. V.P.R.S. Read June 19, 1823. [Phil. Trans. 

 1823,^.400.] 



Adverting to his statement respecting the action of the magnet 

 upon metallic titanium, published in the first part of the Philosophical 

 Transactions for this year, which refers it to adhering iron, Dr. Wol- 

 laston observes, that in subsequent examinations he has found the 

 crystals of that metal slightly attractable, although he had formerly 

 considered them as not thus influenced when apparently perfectly 

 pure. From some comparative trials, however, he finds that the 

 magnetic power thus exhibited would be conferred by the presence 

 of about -rfo-th part of iron alloyed with the titanium ; and there is 

 every reason to suspect that the latter metal might be thus contami- 

 nated. This is rendered additionally probable by the action of tests 

 upon the solutions of the supposed pure titanium; and upon the whole, 

 Dr. Wollaston thinks that we should not be warranted in classing 

 titanium with the magnetic metals. 





