]28 
GrevillEj on New Diatoms. 
occurs of a smaller size in Lake Monroe, at Enterprise, 
Florida ; Bailey. In most of our large Atlantic rivers and 
brackish marshes ; at Cape May, saltmarsh near Cold Springs, 
abundant ; Dr. Lewis. Mouth of the River Berbice, West 
Indies, at half tide ; Dr. Abercrombie. 
Having had occasion some years ago to notice that this 
species exhibited a remarkable range of variation, I have 
endeavoured to ascertain to what extent it may be traced. 
In taking the original figures of the late Professor Bailey as 
our starting-point, we find the longitudinal median space so 
large that the strise are regarded as forming a mere marginal 
band, constituting, in fact, the salient feature in the specific 
character of Bailey, and subsequently of Ralfs. In the 
smaller of the two figures given by the former the median 
space is equal to half the entire breadth of the valve. The 
next American authority is my friend Dr. Lewis, of Phila- 
delphia, who publishes a figure of a singular variety, which, 
he says, is more common on the Delaware River and its 
tributaries than that represented by Bailey, and which, he 
thinks, may be the Navicula Esoos of Kiitzing. (Fig. 21.) 
In this variety the breadth of the median blank space is 
diminished nearly one half. In my two larger figures (18, 
19), drawn from Berbice specimens, the breadth of 
the same part is again considerably reduced ; and in the 
small figure (20) , from the same locality, the blank space has 
become a mere line. Thus,, although the extremes present 
an extraordinary difi^erence, we have the discrepancy recon- 
ciled by intermediate conditions. In a dry state the valve of 
the Berbice examples exhibits very gorgeous colouring, the 
general hue being fine blue, while a broad, bright, crimson 
streak extends down each side midway between the median 
line and the margin, passing into orange-yellow towards the 
ends. It is to be regretted that there should be no reference 
to this in the American notices of the species. Another 
character which is prominent in the Berbice specimens is 
not mentioned by Bailey or Lewis. I refer to the shadowy 
lines, one of which passes down the whole length of the valve 
on each side between the margin and the median line ; the 
other, close to the margin itself, is indistinctly given in Dr. 
Lewis's figure. The former seems to be uncertain|as to its 
position, being much nearer the median in my figure 20 than 
in figures 18 and 19. These lines appear to be caused by 
superficial ridges, the intermediate spaces being generally 
concave ; and if so, the character is an important one. With 
regard to the striation in some large valves, I have counted 
16 in '001''. In some small varietes 25, or even more, in 
