110 My. J. Ralfs on the British Diatomacee. 
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 _ and suffer 
the frustules to escape. 
The frustules are remarkable for ther length, bemg many times 
longer than broad; they are siliceous, simple or bmate, linear, 
not unlike those of Frustulia Una, but their ends are rounded. 
The lateral surfaces in form resemble the front, but are marked 
with numerous transverse striee. 
The endochrome is interrupted at regular mteryals by hyaline 
globules producing a variegated appearance. 
Puate IIL. fig. 1. Homeocladia anglica: a, natural size; b, 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 Homeocladia and Schizonema in haying 
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 longas broad. Grev. Crypt. Fl. tab. 294; Grey. in Hook. 
Br. Fl. vol. ii. p. 416; Ag. Consp. Diatom. p. 24; Harv. Br. Alg. 
p- 209; Kutz. /. c. p. 109. 
Parasitical on Zostera marina and the smaller marine algz, 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 shght 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 mdeed 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- 
