NAVICULA PLICATA. 59 
Navicula plicata, Donkin, n. sp. 
Plate IX. figs. 2a & 2d, 
Frustule on M. V. broad, oblong, slightly constricted in the 
middle, extremities truncate, angles slightly rounded, 
connecting zone traversed by longitudinal lines. V. 
narrow, linear, extremities tapering, obtuse; striz 
‘fine, transverse, reaching to the median line, distinct, 
above 50 in -001". 
I discovered this species in great abundance in a living 
state, in June and July 1869, associated with N. forcipata, 
N. abrupta, N. humerosa, and other marine species, in 
sand-gatherings, in a secluded nook on the sea-shore near 
Warkworth, Northumberland. It is closely allied to N. 
rhombica, Greg., and to N. Auklandica, Grunow (Wien. 
Verh. 1863, p. 151, t. xiv. fig 14); it differs from N. 
rhombica in its longer, much narrower, almost linear valve 
and tapering obtuse extremities, and in its strie, which 
are transverse and of uniform distinctness throughout. 
It resembles N.. Auklandica in size and outline, but differ 
in having much finer striz and the connecting zone desti- 
tute of longitudinal rows of nodules. Grunow describes 
N. Auklandica as having subparallel striz, coarser in the 
middle of the valve and 36 in 001", the connecting zone 
as exhibiting longitudinal lines of transversely elongated 
nodules: he states that it was collected on the sandy beach 
of the Aukland Islands by De Frauenfeld (Exped. Novara) ; 
it will be observed, therefore, that the habitat of this species 
is exactly that of N. plicata. Prof. Gregory doubted 
whether N. rhombica and his N. Libellus are Navicule, 
thinking that possibly they might be found to belong to 
the genus Schizonema : the discovery, however, on the open 
beach of N. plicata by myself in great abundance in a 
