DIATOM ELLA. 



353 



A. Only two false septce. 

 GENUS 66.-DIATOMELLA GREV., 1855. 



Frustules quadrangular, showing only two 

 false septa (vittae), straight and pierced with 

 three openings. Valves linear oblong, fur- 

 nished with a raphe, pseudo-nodules and 

 robust striae. 



A single species. 



Fig. 104. 



Diatomella Balfouriana. 



D. Balfouriana Grev. ! (in Ann. and Mag. Nat. Hist., 1855, 

 P- 259, pi. 9, f. 10-13). 



Valves linear oblong, with apices obtuse-rounded, raphe and terminal 

 nodules, the three openings of the false septa (or underlying diaphragms) 

 showing through ; the two terminal openings round, rather large, the median 

 quadrangular, very large. 



Stria; robust, about 20 in 1 c.d.m., granular. Girdle face quadrangular, 

 with margins (valves) strongly striate, connecting zone smooth ; showing two 

 conspicuous false septa. Length, 1*5 to 3 c.d.m. 



Fresh water. England (W. Sm. |, Scotland (Greville !). 



GENUS 67.-GRAMMATOPHORA EHR, 1839. 



Valves linear or elliptic, sometimes presenting 

 inflations either at the median portion only or also at 

 the apices, very rarely furnished with costae, finely 

 punctate ; pseudo-raphe obscure ; furnished with ter- 

 minal nodules ; no central nodule. Girdle face quad- 

 rangular, elongated, with rounded angles, showing 

 two pairs of false septa, generally undulate or curved, 

 and, in addition, two rudimentary septa arising from 

 woo '' " an internal prolongation of the valve. Frustules 



united in zig-zag. Endochrome granular, sparse. 



Fig. 105. 



Grammatophora 



macilenta. 



var. subtilis. 



