Many other details touching Physiographical characteristics are mentioned as occasion arises in the Alphabetical Gazetteer which follows this Introduction.
"Hertfordshire"
Herbert W Tompkins
I follow him in accepting, with slight modifications of my own, Blanford's Physiographical rather than his zoogeographical regions, not because I think that the latter have been or ought to be superseded so far as the vertebrates are concerned, but rather because the limits of the geographical distribution of aquatic invertebrates appear to depend on different factors from those that affect terrestrial animals or even aquatic vertebrates.
"Freshwater Sponges, Hydroids & Polyzoa"
Nelson Annandale