NAVICULA FORTIS. 57 
extremities, instead of appearing as transverse parallel 
bars. 
Hab. Marine. Lamlash Bay, Isle of Arran, and Loch 
Fine (Prof. Gregory) ; coast of Northumberland, plentiful 
in sand-gatherings (A. S. D.). 
Navicula minor, Gregory. 
Navicula minor, Greg. Diat. of the Clyde, p. 5, pl. i. fig. 1; Ralfs, in 
Prit, Inf, p. 909; Rabenh. Europ. Diat. p.177. 
Plate VIII. figs. 7@ & 7 6. 
Frustule small, on M. V. oblong, constricted in the middle, 
extremities truncate, angles bevelled. V. elliptical, 
lanceolate, extremities acute, slightly acuminated ; 
strie oblique, connivent, distinct, 35 in ‘001", some- 
what shortened in the middle of the valve. 
Hab. Marine. Loch Fine (Prof. Gregory). Tyne- 
mouth, Northumberland, frequent in sand-gatherings 
(A. 8. D.). 
Navicula fortis, Gregory. 
Pinnularia fortis, Greg. Trans. Micr. Soc. n. gs. vol. iv. p. 47, pl. v. 
fig. 19; Rabenh. Europ. Diat. p. 215, 
Navicula fortis, Ralfs, in Prit. Inf. p. 905. 
Plate VIIL figs. 8a, 8b, & 8c, 
Frustule small, on M. V. broad, short, quadrangular, con- 
stricted in the middle, angles slightly rounded, ex- 
tremities truncate. V. broadly lanceolate or lozenge- 
shaped, obtuse; striz reaching to the median line, 
slightly oblique and connivent, coarse and costate, 
about 16 in :001". 
This species is somewhat at variance, in the breadth of 
