T II E A N N A L S 



AND 



MAGAZINE OF NATURAL HISTORY. 



[THIRD SERIES.] 



*' perlitora spargite museum, 



Naiades, et circQm vitreos considite fontes : 

 Pollice virgineo teneros hlc carpite flores : 

 Floribus et pictum, diva*, replete canistrum. 

 At vos, o NymphiB Craterides, ite sub undas ; 

 Ite, recurvato variata corallia trunco 

 Vcllite muscosis e rupibus, ct mihi conchas 

 Ferte, Deaepelagi, et pingui conchylia succo." 



N.Parthenii Giannettasii Eel. 1. 



No. 25. JANUARY I860, 



I. Observations on the Distribution and Habits of the Pelagic 

 and Freshwater Free-floating Diatomacea. By Surgeon G. C. 

 WALLICH, M.D., Retired List, H.M. Indian Forces. 



THERE are three important points connected with the natural 

 history of the Diatomacese upon which the information hitherto 

 recorded appears both scanty and unsatisfactory. These are 



The laws whereby the bathymetrical range of these organisms, 

 in their living state, is determined ; 



The conditions under which their silicious remains are depo- 

 sited and form vast sedimentary strata ; 



And, lastly, the extent and nature of their locomotive powers. 



In the ' Synopsis of British Diatomacese ' (vol. i. Introd. 

 p. xiii.) their distribution and habits are thus described : 



" Their living masses present themselves as coloured fringes 

 attached to larger plants, or forming a covering to stones or 

 rocks in cushion-like tufts, or spread over the surface as delicate 

 velvet, or depositing themselves in a filmy stratum on the sand, 

 or intermixed with the scum of living or decayed vegetation 

 floating on the surface of the water. Their presence may be 

 often detected, without the aid of the microscope, by the absence, 

 in many species, of the fibrous tenacity which distinguishes other 

 plants; and when removed from their natural position, they 



Ann. $ Mag. N. Hist. Ser. 3. Vol. v. 1 



