54 NAVICULE. 
Navicule they form a connecting link; they constitute a 
highly natural group, in which the typical characters of 
Section II. are most highly developed. 
A. Valve lanceolate, linear-lanceolate, or linear ; strie conspicuous, 
costate, or obscurely granular, 
Navicula Northumbrica, Donkin. 
Navicula Northumbrica, Quart. Micr. Journ. n.s, vol. i. p. 9, pl. i. fig. 5; 
Rabenh. Europ. Diat. p. 175. 
Plate VIII. figs. la & 18. 
Frustule on M. V. very broad, quadrangular, slightly con- 
stricted in the middle, central nodules prominent, ex- 
tremities truncate with slightly rounded angles. V. 
very narrow, lanceolate, acute; striz transverse, ob- 
scurely granular, about 28 in ‘001", those opposite the 
central nodule coarser, opaque, and slightly convergent. 
The lateral compression of the valve in this species is so 
great that the distance between the two margins is less 
than that between the margin and the median line; conse- 
quently it is difficult to obtain a S. V. of the valve, which 
generally presents only one of its sides for observation. 
Hab. Marine. Cresswell, Tynemouth, and other locali- 
ties on the sandy beach of Northumberland: abundant. 
Cumbrae, Clyde ; and Teignmouth, 8. Devon (Prof. Walker 
Arnott). 
Navicula inflexa, Gregory. 
Pinnularia infleva, Greg. Trans. Micr. Soc. n.s. vol. iv. p. 48, pl. v. 
fig. 20; Rabenh. Europ. Diat. p. 218. 
Navicula inflera, Ralfs, in Prit. Inf. p. 905. 
Plate VIII. figs. 2a & 20. 
Frustule small, on M. V. broad, constricted in the middle, 
