126 
GrevillEj on New Diatoms. 
fig. 2). Nevertheless^ these two diatoms may be ultimately 
found to be extreme forms of one . and the same species. 
Fig. 11 exhibits a front view of two frustules in situ. 
COCCONEIS. 
Cocconeis armata, n. sp., Grev. — Small ; disc broadly oval_, 
with rather large, subremote^ decussating granules_, and 
distant marginal tubercles; median line straight, with a 
parallel row of very minute close puncta on each side. 
Length -0021". (Fig. 13.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. ; extremely rare. 
A brilliant and well-marked little diatom. The median 
line very slender. The granules arranged in intersecting 
curves, 8 in '001'^ Marginal tubercles, about 8 on each 
side. 
Navicula. 
Navicula strangulata, n. sp., Grev. — Valve elongated, 
deeply constricted at the middle, and composed of two ovato- 
cuneate subacute lobes, very minutely punctato-striate, with 
a narrow border of larger, more remote strise (or cellules) , 
Length •0042'\ (Fig. 24.) 
Hab. In marine dredgings, Nassau, West Indies. 
Among the multitude of described Naviculce I can find no 
trace of this or the following well-marked species. The 
present diatom is evidently allied to N. marginata of Lewis, 
not only in form^ bnt in the contrast between the minutely 
punctate striae of the general surface and the row of larger 
cellules which constitute the margin. In the diatom before 
us these cellules are relatively much smaller than in N. mar- 
ginata, but they are, nevertheless, evident. The general 
striae are almost parallel, becoming slightly oblique only 
towards the ends. These strise, taken near the median line, 
are 20 in '001'', while those at the margin (cellules) are 10 
in -001". 
Navicula Jamaicensis, n. sp., Grev. — Elongated, with a 
deep constriction, dividing the valve into two oblong- elliptical 
lobes, somewhat produced and obtuse at the ends ; structure 
minutely punctate, the puncta (cellules) arranged quincun- 
cially, with a row of still smaller puncta along the margin. 
Length -0010". (Fig. 23.) 
Hab. Jamaica ; obtained by washing seaweeds. 
