Genus 19. NA VIC ULA, Bory.
Frustules free, oblong or lanceolate ; valves convex, with a median
longitudinal line and nodules at centre and extremities, striated ;
striæ resolvable into circular dots.
In the present work, the genus Navicula of Kiitzing is divided into
three ; viz. Navicula, Pinnularia, and Pleurosigma. Stauroneis has
already been placed apart both by Ehrenberg and Kiitzing.
The four genera are, I think, sufficiently distinguished from each
other ; Navicula, by the delicacy of its striæ and their moniliform
character ; Pinnularia, by the confluent nature of the cellular structure
of its epiderm, which gives to its striæ the appearance of distinct ribs
or costæ ; Stauroneis, by the absence of a central nodule, which is
supplied by a band of silex (Stauros) crossing the valve at right
angles to the median line ; and Pleurosigma, by the characteristic
curve of its beautiful frustules.
In a few cases we meet w'ith the semblance of a Stauros in the
genus Pinnularia-, hut in these instances a closer examination will
show that this appearance arises from the interruption of the costæ
merely, and not from the dilatation of the central nodule, which is
still found unchanged.
Sec t . I. Valves lanceolate.
1. Navicula rhomboïdes, V. nearly quadrangular ; striæ very
faint, parallel, 85 in '001". Length -0022" to -0037". v.v.
Ehr. in Kiitz. Bacill. xxviii. 45, xxx. 44, sic Prof. Kiitzing in lit. 1851.
Fresh water. Boggy pools, Sept. 1849, W. Sm. Lancashire, Mr. Johnson,
Aug. 1851. Ben M“ Dhui, at an elevation of 3000 feet, Mr. P. Grant.
Plate XVI. 129.
2. Navicula lanceolata, Kütz. V. lanceolate or elliptical-lanceolate ;
striæ parallel,-44 in OOl". L e n g th -0012" t o -0020". v.v.
Kütz. Bacill. xxviii. 38. xxx. 48 ?
Freshwater. Newhaven, Sussex, Dec. 1852, W. Sm. Dolgelly Earth.
Supp. Plate XXXI. 272.
3. Navicula Crassinervia, Bréb. V. elliptical-lanceolate ; extremities
produced ; striæ obscure. Length '0013" to •0026". v.s.
“ Navicula Crassinervia,” ad specimina sub hoc nomine quæ misit cl. De
Brébisson, Sept. 1852.
Fresh water. Wareham, Sept. 1849, W. Sm. Snow Mud, Grampians,
Dr. Dickie. Dolgelly, Mr. Ralfs.
Supp. Plate XXXI. 271.
4. Navicula serians, Kütz. V. acute ; transverse striæ faint, 60 in
•001"; longitudinal distinct, 36 in •OOl"; frustules frequently cohering.
Length •0017" to -0035". v.v.
Kiitz. Bacill. xxviii. 43, xxx. 23, ad specimina quæ communicavit cl. De
Brébisson in lit. Sept. 1852.
Fresh water : boggy pools. Wareham, Sept. 1849, IF. Sm. Forest Row,
Sussex, Mr. Jenner, Jan. 1844. Ben M‘ Dhui, at an elevation of 3000 feet,
Mr. P. Grant. Lough Island-Reavey Deposit. (Lapland.)
Plate XVI. 130.
5. Navicula cuspidata, Kütz. V. acute; striæ parallel, distinct,
36 in -001". Length -0027" to -0062". v.v.
Kütz. Bacill. ill. 24 & 37. ad specim. authen. quæ misit amie. De Brebisson.
Navícula fulva, Ehr. Inf. xiii. 6.
Fresh water; ditches. Lewes, Sept. 1850, IF. Sm. Guildford, Mr. Capron.
Belfast, Dr. Dickie. Cantyre Peat. Lough Mourne and Peterhead Deposits.
Plate XVI. 131.
6. Navicula rhynchocephala, Kütz. V. acute ; extremities produced,
linear; striæ distinct, radiate, 24 in •OOl". v.s.
Kütz. Bacill. XXX. 35 ?
Fresh water. Belfast, Dr. Diclde.
Plate XVI. 132.