NAVICULA HUMILIS. 67 
rounded. V. linear, slightly dilated at the middle 
and near the rounded extremities; striz coarse, 
costate, very oblique, diverging midway between the 
central and terminal nodules, reaching to the median 
line, much shortened around the central nodule, so as 
to leave a large orbicular median blank space, 25 in 
001". 
This large and beautiful species is readily distinguished 
from N. rectangulata, Greg., by its larger size, more oblique 
striz, and large orbicular blank space around the central 
nodule, and more especially by the peculiarly curved appear- 
ance imparted to the median line by the great convexity 
of the valve near the extremities, and its depression in the 
middle; it was discovered by me at Cresswell, North- 
umberland, in June 1857, and dedicated to my friend Sir 
W. C. Trevelyan, Bart., of Nettlecombe, Somersetshire, 
and of Wallington, Northumberland. 
Hab. Marine. Cresswell, Linemouth, and Boulmar, 
Northumberland, frequent in sand-gatherings (A. S. D.). 
Navicula humilis, Donkin, n. sp. 
Navicula varians, var., Greg. Trans. Micr. Soc. n. 8, vol. iii, pl. ii, 
figs. 20 & 208. 
Navicula inflata, var., Greg. Trans. Mier, Soc. n. 8, vol. iii. pl. ii. fig, 20. 
Plate X. figs. 7a & 70. 
Frustule minute, on M.V. broad, quadrate, constricted in 
the middle, extremities rotund-truncate, angles pro- 
minent, central nodules projecting. VV. linear, much 
inflated in the middle, extremities broadly rounded 
and tumid; strie reaching to the median line, con- 
vergent, coarse, costate, and very conspicuous. 
This is the only freshwater species with which I am 
