PLOIARIA. 



457 



b. 

 Fig. 185. Corinna elegans. 



a. Valve view. b. Girdle view. t. Filament. 



The true Hemiauhts, of which more than 70 species are recorded, is rarely 

 found in a living state. Some few species, such as H. Heibergii, meinbranacea 

 and Hauckii have been so found in the Java Sea and the Adriatic, but the 

 remainder are fossils, the greater number being found in the deposits of Mors, 

 Baibadoes, Simbirsk, Oamaru, &c. The true type-forms belonging to the 

 three other sub-genera have not yet been found elsewhere than in the deposit 

 of the Island of Mors. 



The Hemiaulus are large diatoms with strong silica ; they form very 

 interesting objects when viewed as a dry preparation with dark ground 

 illumination under a low power objective and a binocular microscope. This 

 is the best means which a beginner can employ in order to obtain a good idea 

 of what a diatom really is. 



GENUS 122,-PLOIARIA PANT., 1889. 



a. b. 



Fig. 186. 



Ploia ria peiasiform is. 



a. Girdle view. b. Valve view. 



Valve lanceolate, elliptic, with apices 

 broadly rostrate, puncta well marked and 

 distinct, valve convex in prirdle view and 

 median portion abruptly inflated, almost 

 hemispherical. 



A single species. 



