46 NAVICULE. 
tial features—by the median constriction of the valve and 
by the division of the strie into an outer conspicuous, and an 
inner fainter section, by an intersecting longitudinal groove ; 
this latter character connects them with Division A of 
Subsection I., in which it is also developed, especially in 
N. lineata and N. suborbicularis. 
Navicula Crabro, Ehrenberg. 
Navicula Crabro, Ehren. in Kiitz. Spec. Alg. p. 83; Sm. Synop. vol. 
ii, p. 94; Ralfs, in Prit. Inf. p. 804; Rabenh. Europ. Diat. 
p. 204. 
Navicula pandura, Bréb. Diat. de Cherb. fig. 4; Greg. Trans. Mier. 
Soc. n. 8, vol. iv. p. 43, pl. v. fig. 11; Ralfs, in Prit. Inf, 893. 
Navicula nitida, Greg. Trans. Micr. Soc. n. s, vol. iv. p. 44, pl. v. figs. 
12 & 12%, 
Navicula didyma, costate var., Greg. Trans. Micr. Soc, n.s. vol. iv. p. 45, 
pl. v. fig. 15. 
Pinnularia Crabro, Ehren. Berlin, 1844; Rabenh. Europ. Diat. p. 219. 
Pinnularia pandura, Bréb., var, 8. elongata, Greg. Diat. of the Clyde, 
p. 17, pl. i. fig. 22. 
Diploneis Crabro, Ehren. Mikrogeo. t. xix. fig. 29. 
Plate VII. figs. la & 18. 
Frustule large. V. panduriform, with cuneate, obtuse 
extremities ; striz subparallel, nearly transverse, cos- 
tate, or obscurely granular, coarse, about 11 in ‘001", 
interrupted by a straight longitudinal groove into a 
broad outer and a narrow inner section, the latter 
consisting of a longitudinal row of conspicuous hemi- 
spherical nodules. 
No better illustration than this species could be 
selected to show the necessity for abolishing the genus 
Pinnularia, and the confusion its establishment has created. 
It will be seen by the synonyms given that N. Crabro has 
been placed in the genus Navicula by some observers and 
in Pinnularia by others, while by others, again, it has been 
referred to both these genera. It is subject to considerable 
