110 Mr. J. Ralfs on the British Diatomacese. 



The frustules are numerous, and either scattered or collected 

 in bundles, between which the frond is somewhat contracted. 

 The extremities of the frond finally become ruptured and suffer 

 the frustules to escape. 



The frustules are remarkable for their length, being many times 

 longer than broad ; they are siliceous, simple or binate, linear, 

 not unlike those of Frustulia Ulna, but their ends are rounded. 

 The lateral surfaces in form resemble the front, but are marked 

 with numerous transverse strise. 



The endochrome is interrupted at regular intervals by hyaline 

 globules producing a variegated appearance. 



Plate III. fig, 1. Homoeocladia anglica: a, natural size; h, portion of 

 a filament magnified ; c, front view of frustule ; d, lateral view of empty 

 frustule. 



Berkeleya, Grev. 



Frustules linear, included within tubular submembranaceous fila- 

 ments which are free at one extremity, but have the other im- 

 mersed in a gelatinous tubercle. 



This genus differs from Homceocladia and Bchizonema in having 

 the base of the filaments immersed in a tubercle. 



1. B.fragilis, Grev. Filaments subsimple, minute; frustules nu- 

 merous, crowded, lanceolate or linear-lanceolate, eight to twelve 

 times as long as broad. Grev. Crypt. Fl. tab. 294 ; Grev. in Hook. 

 Br. Fl. vol. ii. p. 416 ; Ag. Consp. Diatom, p. 24 ; Harv. Br. Alg. 

 p. 209; Kiitz. I.e. p. 109. 

 Parasitical on Zostera marina and the smaller marine algae, also on 



rocks in the sea ; November. 



Southampton, Miss Hill ; Mount's Bay, J. R. ; Ireland, Mr. 

 M'Calla, according to a specimen from Dr. Scouler. 



When recent this plant is dark olive-brown with a slight lustre ; 

 when dried it becomes greener, and is generally glossy. 



The filaments are very short, seldom exceeding a quarter of an 

 inch in length, and pale at their immersed base. They issue 

 from the tubercle in a penicillate or radiate manner, and though 

 usually simple are occasionally dichotomous at their origin. 



The tubercle is colourless and large in proportion to the size 

 of the plant. It is more diffuse in those growing upon rocks 

 than in parasitic ones, sometimes indeed to so great a degree 

 as to lose the appearance of a tubercle. It is always gelatinous, 

 is easily broken, and if put into fresh water very soon becomes 

 partially dissolved, and thus allows the separation of the fila- 

 ments. 



Under the microscope the filaments are hyaline and slightly 

 crenate at the margin ; the frustules are simple or binate, nume- 

 rous, crowded, often confined to the middle of the filament, elon- 



