28 NAVICULE. 
late, with rounded extremities ; striz slightly oblique, 
close, and delicate, 36 in 001". 
This species and the preceding are frequently found 
associated in subalpine localities, especially in lacustrine 
habitats. Both are abundant in a lacustrine deposit from 
Loch Oich on the Caledonian Canal, supplied to me by 
Mr. Hennedy. 
Hab. Fresh water. North-west of Scotland, frequent ; 
Loch-Oich deposit, Caledonian Canal (A. S. D.); Marl, 
Co. Down (Prof. Smith). 
Subsection IV. Valve oblong, linear-elliptical, or linear, with 
rounded or cuneate extremities ; strice fine, transverse, reach- 
ing to the median line. 
Navicula levissima, Kiitzing. 
Navicula levissima, Kiitz. Bac. p. 96, t. xxi. fig. 14; Ralfa, in Prit. Inf. 
p. 895; Sm. Synop. vol. ii. p. 91; Rabenh. Europ. Diat. 
p. 188. 
Stauroneis rectangularis, Greg. Quart. Micr. Journ. vol. ii. p. 99, pl: iv. 
fig. 17. 
Plate V. fig. 2. 
Frustule small. V. hyaline, colourless, linear, sometimes 
slightly inflated in the middle, extremities flattened 
and slightly rounded; striz fine, delicate, about 50 
in ‘001’, transverse, reaching to the median line; 
median line and nodules distinct. 
The appearance of a stauros, as delineated in Prof. Gre- 
gory’s figure, observable on this species when seen by a 
medium magnifying-power, is deceptive; the strize reach 
to the central nodule. 
Hab. Fresh water: frequent. 
