1881.] On certain points in the Anatomy of Chiton. 121 



and at last to red-brown, the colour of oxide ; it loses in average 8 to 

 9 per cent, sulphuric acid with combined water. When dissolved in 

 boiling hydrochloric acid a snow-white residuum is obtained, which, 

 under the microscope, proves to be composed of extremely well-pre- 

 served shells of microscopic Radiolaria, belonging to different genera. 

 The size of those mostly regular globular bodies ranges between 

 O045 millim. and - 1135 millim. The quantity of this residuum 

 amounts in a mean of three trials to 25 per cent. The quantity of 

 soluble substance is therefore 73 per cent., if we take away 2 per 

 cent, hygroscopic water. This soluble substance is pure sulphate of 

 oxide of iron with a very small amount of sulphate of alumina. The 

 quantity of the sulphuric acid in the mineral was directly determined 

 by precipitation of the hydrochloric solution of the mineral with 

 chloride of barium. 2,000 mgrms. of the mineral gave 1,250 mgrms. 

 sulphate of baryta, corresponding to 431 mgrms. sulphuric acid. The 

 amount of this acid in the mineral is therefore 21*5 per cent. The 

 quantity of the oxide with a small amount of alumina is 51 '5 per 

 cent., corresponding to 36 per cent, metallic iron. 



~No traces of copper or any other metal have been found in the 

 mineral; a trace of arsenic, however, is observed, as is shown by- 

 means of the copper-arsenic test, by boiling the hydrochloric solution 

 with a clean copper slip, which becomes coated with a thin deposit of 

 metallic arsenic. 



Cyprusit is composed as follows : — 



Oxide of iron, with a very small amount of alumina 51 '5 



Sulphuric acid 21*5 



Insoluble siliceous substance 25 



Hygroscopic water 2 



100-0 



V. " On certain points in the Anatomy of Chiton." By Adam 

 Sedgwick, M.A., Fellow of Trinity College, Cambridge. 

 Communicated by F. Maitland Balfour, F.R.S. Received 

 November 5, 1881. 



An account of the structure of the kidney of Chiton has long been 

 a want in morphology. Middendorif,* in 1848, described a branched 

 gland lying ventrally on each side of the body cavity which he identi- 

 fied as kidney ; but he records no observation on the structure of the 



objects belonging to natural history derived from Cyprus I add a new one ; the 

 mineral would bear the name " Cyprusit." 



* " Memoires de l'Acad. de St. Petersbourg," 6th ser., vol. vi. 



K 2 



