Fragilariece.'] exilaeia. 335 



where it seems very abundant, rendering Tolysiplionia 

 nigrescens quite hoary. The filaments are composed of 

 oblique-angled frustules, curling up in a curious manner -, 

 and when seen through a lens, each portion is elegantly 

 reticulated. 



Genus CII. DIATOMA. 



Gen. Char, filaments composed of rectangular frustules, 

 cohering at the angles, and finally separating. 



1 . DiATOMA MAHiNUM, Lyuglye. 



Hab. Parasitic on marine Algee in spring. Greenish 

 when fresh; powdery and pale when dry. Common in 

 most places ; but rare on the coast of Ayrshire, » where its 

 place is occupied by Striatella. 



Genus CUT. EXILAEIA, Greville. 



Gen. Char. Frustules rectilinear, fasciculate, or spreading in 

 fan-shaped series, fixed at the base to a receptacle or stipes. — 

 Greville. 



1. ExiLARiA FULGENS, GrevUle. 



Hab. Parasitic on marine filiform Algee. Devonshire, 

 Mrs. Griffiths; Appiii, Captain Carmichacl; Arran and 

 Ayrshire, D. L. ; Lcith, D. L., jun. 



