152 Clarence J. Elmore 



GLOSSARY 



Ala. PI. alae. A wing. The same as carina or keel, in Surirella, 



etc. 

 Auxospore. The spore formed by the union of two cells, or the 



excessive growth of a single cell forming a new diatom larger 



than the parents. 

 Carina. Keel ; the wing-like projection on a diatom valve. 

 Connecting zone. The portion of a diatom cell wall between the 



valves ; the girdle. 

 Convergent. Pointing toward raphe at the ends, as the striations 



in some species of Navicula. 

 Costa. A rib ; heavy markings on a diatom valve not consisting 



of rows of dots. 

 Decussate. From Lat. dccussatus, crossed at acute angles like 



the letter X. Crossing one another in three directions as the 



striations in some species of Gyros'igma. 

 Diatomin. The coloring matter of diatoms. It is composed of 



phycoxanthin and chlorophyll. 

 Dorsal. The back, or outer side of a curved diatom. 

 Endochrome. The chromataphore of a diatom. 

 Frustule. An entire diatom cell including the valves, girdle, and 



contents. 

 Fenestrated. (Lat. fenestra, window.) With window-like open- 

 ings. 

 Girdle. The portion of a diatom cell wall that connects the valves. 

 Interzone. A band between the portion of the girdles attached to 



each valve. In some genera there are no interzones ; in others, 



one ; and in others, two or more. 

 Keel. The same as carina. A wing-like projection on a diatom 



valve. 

 Lumen. A clear space at the margin and ends of a diatom cell 



caused by a thickening of the wall ; seen in some species of 



Stauroneis. 

 Naviculoid. Shaped like a Navicula; boat-shape. 

 Nodule. A thickening in a diatom valve. In Navicula, for ex- 

 ample, the nodules appear as dots in the center and at the ends. 



