32 
DoNKiN, on Marine Diatomacece. 
Navicula. 
17. N. lineata, n. sp. — Form of S. V. linear -elliptical^ oc- 
casionally constricted a little in the middle. Striae distinct,, 
costate, and interrupted in the middle by a longitudinal, 
transparent line^ running from one extremity of the valve to 
the other, nearly parallel with its margin; strise also cut 
short, some distance from the median line, by another trans- 
parent longitudinal line parallel to the last, and succeeded by 
a line of indistinct punctse. Median line broad, and bounded 
on either side by a narrow, rectilinear, transparent line. 
Length from 0'0023" to 0-0035" ; breadth from 0-0008" to 
0-0013". Valve brown in balsam. 
This species is easily recognised from N. didyma and its 
varieties by its costate, bisected strise, and by the much larger 
blank space on either side of the median line ; the constric- 
tion of the valve, when it exists, is also much slighter. Each 
half of the valve is divided into three distinct, narrow com- 
partments, by three transparent lines running longitudinally 
between the extremities ; the two outer being parallel to each 
other and to the margin, . and the inner parallel to the con- 
tiguous median line. The two outer compartments each 
inclose a band of strise, while the third or inner is hyaline, 
and bordered by a longitudinal row of indistinct transverse 
punctse. 
Hab. Cresswell Bay and Linemouth, abundant ; not general 
in its distribution. 
18. N. (Estiva, n. sp. — Form gracefully elliptical ; colour of 
dry valve blue, in balsam brown. Strise fine, distinct, costate, 
or very obscurely moniliform, reaching close to the median 
line, and crossed a short distance on either side of it by a 
narrow, opaque, longitudinal line. Length from 0*0026" to 
0-0045'^; breadth from 0-0012" to 0-0022". 
This large and very beautiful species differs from N. Smithii 
in its much more gracefully elliptical figure, in its costate and 
much finer strise, and in the much darker brown colour of 
the valve when mounted in balsam. N. Smithii, as it occurs 
on the Northumbrian shore, is a much smaller species, with 
rather coarse, moniliform strise, and is nearly colourless in 
balsam when examined with a low power ; it is likewise much 
more general in its distribution than the present species, and 
occurs in every strictly marine gathering which I have made. 
Hab. At Cresswell and Linemouth, abundant. 
Postscript. 
Since the preceding pages were read before the Micro- 
