Dr Greville on New Genera and Species of Diatoms. 35 
Frustules much elongated, from ‘0055” to 0100", the 
breadth scarcely more than ‘0004". Front view linear, 
rectangular, with two longitudinal rows of brilliant puncta 
in pairs, at some distance from the margin, the space 
between the rows and the margin very finely striated, while 
that between the rows forms a smooth, blank line. Lateral 
view linear, slightly dilated at the middle, and generally, 
also, more or less at the rounded ends, with a median line, 
aud terminal and central nodules, the line being situated 
slightly nearer to one side than the other ; transverse septa 
pervious, strong, subequidistant, numerous, upwards of 
twenty in the shorter frustules, nearly double that number 
in the longest; very fine transverse striz also cover the 
whole space. Besides the above front and lateral views, 
the valve must be noticed separately, being distinguished 
by the median line and nodules and the fine striz only, 
and is so thin and transparent that it is easily overlooked. 
The septa belong to an internal arrangement, being per- 
ceived in the front view to be placed at about a third of 
the entire breadth of the frustule from each side, or, in 
other words, from the valve. The puncta, which shine 
like brilliant points of light, are of course the sutural ter- 
minations of the septa viewed vertically. The shorter 
figures are from the Harvey Bay dredging, the long one 
from New California. 
PLAGIOGRAMMA. 
Plagiogramma costatum, n. sp., Grev.—F ront view with 
nearly straight sides and sharp angles; valves lanceolate, 
with two centrical vitte; strie costate, pervious, 10 in 001”. 
Length about -0030" (figs. 5, 6). 
Hab. New Caledonia ; in a dredging communicated by Dr 
Roberts. 
This species is well distinguished by its clear costation 
and central pair of vitte. It is by no means unfrequent in 
the dredging. 
Plagiogramma spectabile, n. sp., Grev.— Valves constricted 
in the middle, then dilated and slightly lyriform ; vitte 
- numerous (about twelve), with intermediate transverse lines 
of minute puncta. Length about 0080". (fig. 7). 
