3G BRITISH DIATOM AC E.42. 



ose; annuli 5 to 9, 12 in -001"; septa entire, alternate, increasing 

 in length as they recede from the valves ; valve, in smaller frustules, 

 elliptical, in larger, with a slight inflation in the centre, and pro- 

 duced and linear ends; striae reaching the extremities of valve, 19 

 in -001". Breadth of filament -0006" to -0029". Breadth of valve 

 •0003" to -0005". v.v. 



Kxitz. Bacill. xxi. ii. 4. Fragilaria striatula, Grev. B. F. p. 403. ad specim. 

 authen. in herb. Grev. Fragilaria Carmichaelii, Harv. Man. p. 198. 

 Tessella Catena, Ralfs, Ann. vol. 12. p. ii. 1. ad specim. authen. in herb. 

 Jenn. 



Marine. Seaford, Sussex, March 1852. Lancing, Sussex, Aug. and Nov. 

 1853, W. Sm. Swansea, Mr. Ralfs. Frith of Clyde, Feb. 1854, Mr. R. 

 Hennedy. 



Plate XXXVIII. 306. 



Genus 40. STRIATELLA, Ag. 



Filament compressed, stipitate ; frustules imperfectly siliceous, annu- 

 late, indefinite, annuli plane; valves elliptical-lanceolate, with a 

 median line, striated. 



The stipes, which is longer in this genus than in any other of the 

 filamentous Diatomacese, is a feature which cannot be overlooked ; 

 and the imperfectly siliceous nature of the frustules, the non-cellulate 

 structure of the annuli, and the slight projection of the septa, which 

 increase a little in length as they recede from the valves, sufficiently 

 characterize the only species which has hitherto been detected. 



The specific name is derived from the appearance of the endo- 

 chrome, which in the living specimen is invariably collected in a 

 central mass, with slender threads radiating in all directions towards 

 the cell -wall. 



The coherence of the frustules is easily disturbed, and it is not 

 unusual to find some filaments in which an imperfect zigzag has been 

 formed ; in such cases a slight accumulation of mucus takes place at 

 the cohering angles. The filaments are ordinarily, however, direct 

 and continuous, and rarely consist of more than three or four, fre- 

 quently of only two frustules, in which respect Striatella differs from 

 Rhabdonema and the other allied genera, in which the filaments ordi- 

 narily contain twenty frustules or more. 



