410 DIATOMACEJE. 



Mr. Ralfs. Pond near Wormley, West End, Herts : 

 A. H. H. 



The greatest peculiarity of this species is, that frequently 

 the frustules cohere together in considerable numbers, so as 

 to form filaments apparently similar to those of Fragilaria, 

 but in all probability really distinct. If, however, the speci- 

 mens be dried or kept in water, these filaments will generally 

 be found broken up in the manner of a Diatoma. 



The only species with which it needs to be contrasted is 

 Diatoma vulgaris, from which it may be distinguished by the 

 absence, or at all events the exceeding fineness of the strias, 

 on the end surfaces of the frustule, as well as by the fila- 

 ments, which it usually forms. 



The colour is stated to be green, not altering much in dry- 

 ing. In my specimens it has been dark brown, changing to 

 a greenish hue in the herbarium. 



The removal of this species from Fragilaria to Diatoma 

 will render that genus a natural and not an anomalous one. 



71. BACILLARIA Gmelin. 



Char. Frustules sliding one upon the other. 

 Derivation. From bacillum, a small stick. 



In the genus Bacillaria Ehrenberg includes not merely 

 the species of the two preceding genera, but likewise the sin- 

 gular production which forms the type of the limited genus 

 Bacillaria. 



1. BACILLAKIA PARADOXA Gmelin. 

 Plate XCII1. Fig. 10. 



Char. Frustules very many times broader than long, cohering 

 together in considerable numbers upon the same plane, 

 motive upon each other. In end view striated. 

 F. sonderbares Stabgenthier Miiller, Muller's Kleine 



