BRITISH DTATOMACE^E. 67 



Genus 53. BERKELEYA, Grev. 



Frond gelatinous, definite, tuberculate at base, emitting towards its 

 circumference filaments enclosing the densely-packed frustules; 

 frustules naviculoid ; valves linear-lanceolate, obtuse. 



1. Berkeleya fragilis, Grev. Stria? obscure. Length of frond • 2" 

 to -6". Length of frustule '0015" to -0035". Breadth of valve 

 •0003". v.v. 



Grev. S. C. F. tab. 294. Grev. B. F. p. 416. Ralfs, Ann. 1 ser. vol. 16. pi. iii. 2. 

 Kiitz. Bacill. p. 109 ; Sp.Alg. p. 96. Berkeleya Adriatica, Kiitz. Bacill. 

 xxii. 4 ; Sp. Alg. p. 96. ad spec, authen. quae misit am. De Brebisson. 

 Prit. Anim. xvii. 34 & 35. 



Marine. Torbay, Mrs. Griffiths. Cumbrae, Sept. 1853, Mr. Hennedy ; 

 and Oct. 1854, Dr. Arnott. Cork Harbour, Oct. 1855, W. Sm. (Cherbourg, 

 M. Be Brebisson. Montredon near Marseilles, May 1854, W. Stn.) 



The tuberculate character of the frond in the present genus seems to arise 

 from the adherence of the gelatinous filaments towards their bases, and is 

 more or less distinct at different stages of the plant's growth. In an advanced 

 state the adherence is less conspicuous, and the entire frond becomes fila- 

 mentous. The two species given by Kiitzing have apparently owed their 

 determination to this circumstance, as I can find nothing in the structure or 

 character of the frustules to warrant the separation of B. Adriatica from 

 our native form. The genus is sufficiently distinguished from its allies by 

 the form, arrangement and structure of its frustules, which cannot be con- 

 founded with those of the filamentous species afterwards to be described. 

 The valves are striated, as is evident from their colour, which is a very pale 

 straw ; but I have not been able to resolve the striae so as to ascertain their 

 aumber. 



Plate LIV. 344. 



Genus 54. ENCYONEMA, Kiitz. 



Frond filamentous, tubular, sparingly divided ; frustules cymbelloid ; 

 valves convex, striated ; striae moniliform. 



The frustules of the present genus so closely resemble those of 

 Cymbella, that a superficial observer would fail to detect their true 

 character in a prepared gathering. A careful inspection would, how- 



F 2 



