4. NAVICULEZ. 
with a central and terminal inflations, extremities 
cuneate and subacute, or rounded ; striz reaching to 
the median line, transverse, fine and delicate; dry 
valve yellowish brown. 
The great variation im size and outline to which this 
species is subject has caused it to be described under the 
various synonyms given above. Kiitzing seems to have 
relied on size and outline in separating N. gibberula as a 
species distinct from N. limosa. 
Hab. Fresh water: common and very generally distri- 
buted. 
Navicula ventricosa, Ehrenberg. 
Navicula ventricosa, Ehren. Kreidethierchen, 1839, t. iv. fig. 10; Kiitz. 
Bac. p. 99, t. xxi. fig. 15. 
Plate XII. fig. 7. 
Frustule small, oblong. V. highly convex, linear, inflated 
in the middle ; extremities slightly tumid and rounded ; 
striz reaching to the median line, transverse, fine and 
delicate, absent opposite the central nodule. 
This species is distinguished from the preceding, with 
which it has evidently been confounded, by its smaller size 
and the blank unstriated space opposite the central nodule. 
It agrees with the figure of N. ventricosa, Ehren. given by 
Kiitzing, to which I have referred it, to prevent the intro- 
duction of a new name. 
Had. Fresh water: frequent in elevated situations. 
Sweethope Lough, Northumberland ; Loch-Oich deposit. 
