DIATOM ACEjE I FAMILY MEEIDIEjE. 



291 



in Epiihemia they are very commonly adherent by the flat or 

 concave surface of the connecting zone ; and in Himantidium they 

 are usually united into ribbon-like filaments. — In the Family 

 Meridiece we find a similar union of the transversely-striated indi- 

 vidual frustules ; but these are narrower at one end than at the 

 other, so as to have a cuneate or wedge -like form ; and are 

 regularly disposed with their corresponding extremities always 

 pointing in the same direction, so that the filament is curved 

 instead of straight, as in the beautiful Meridion circulate (Fig. 124). 

 Although this plant, when gathered and placed under the micro- 



Fig. 126. 



Licmophora flabellata. 



scope, presents the appearance of circles overlying one another, 

 it really grows in a helical (screw-like) form, making several conti- 

 nuous turns. This Diatom abounds in many localities in this 

 country ; but there is none in which it presents itself in such 

 rich luxuriance as in the mountain-brooks about West Point in the 

 United States, the bottoms of which, according to Prof. Bailey, 



u 2 



