362 



STRIATELLA. 



GENUS 73. STRIATELLA AGARDH, 1832. 



Valves lanceolate or linear elliptic, furnished with a pseudo-raphe 

 usually distinct, without costae ; striae excessively delicate. Girdle 

 face showing a large number of false septa. Frustules very slightly 

 silicious, longly stipitate. 



Endochrome granular, radiant around a central point. 



Fig. 113. Striatella unipunctata. 



Fig. 114. 



Striatella delicatula. 



var. rectangulata. 



F 'g- "5- 

 Striatella interrupta. 



The genus Striatella, as at present constituted, 

 results from the fusion of three former genera : 



i. Striatella Ag. (fig. 113), septa continued 

 throughout the girdle face of the frustule. 



2. Hyalosira Kiitz. (fig. 114), septa appear- 

 ing alternately, interrupted at their apex. 



3. Tessella Ehr. (fig. 115), septa interrupted 

 in the middle of their length. 



About a dozen species have been described, 

 but only the following are found in the North 

 Sea : 



ANALYSIS OF SPECIES. 



f Septa continued throughout the length of the girdle face, size considerable S. unipunctata. 



-! Septa appearing ( Size small, septa scarcely visible . . S. delicatula. 



alternate, < 



L interrupted. (.Size medium, septa clearly visible . . . S. interrupta. 



