YMKKSIIIKK NATlliAI.ISTS UNlUN. 
The Diatomaceae and Desmidiaceae in their geographical dis- 
tribution are also perfectly in hainiony with all other groups and 
strikingly display the results of the doniinancy of Diatomic life and 
the regressive and feebler character of the Desniids in the relative 
))Osition they occu})y, for, according to Prof. (t. S. West, it is established 
that the pools, lakes, and ponds situate upon the more lowland parts 
of the country, and rich in dissolved mineral salts derived from the 
newer and softer Tertiary strata, are almost c()mj)letely m()noi)olized 
by Didtomdced', while the Det^mldhicnc are quite scarce or absent. 
VI. Map illustrating the geographical di.strihulioii (jf l^ialonis and iJesniids in ttie 
l>ritish I>les, and sliowing Us essential similarity to that of the coleoptera and other forms of life. 
rhe Rku represents the areas dominated by Diatomaceons life and Hi.uk that in which tlie 
more regressive and weaker Desmidiacea; are still pre-eminent. 
On the contrary, the areas richest in Desmidian life correspond 
geographically with the outcrop of rocks of Palaeozoic or Precambrian 
age in the mountainous regions of England, Wales, Scotland, and 
Ireland, where the waters of the lochs and pools are veiy ])ure and 
clear, and almost deficient of dissolved mineral salts. In such 
