A
t i <
It ®,
i ¡
IP;
front view ; straight, attenuated at either end in lateral
as^ject.
Bacillaria sigmoidea Nitzsch, Beiträge z. Infusorienhunde,
1817 (1816), p. 104. Cymhella sigmoidea Agardh,
Consp. Crit. Diatom. 1830, p. 11. Frustidia Nitzschii
Kiitz., Linnæa, 1833, p. 554. t. xiv. fig. 33. Navicula
sigmoidea Ehr., Die Infus. p. 182. t. xiii. f. 15. t. xxi.
f. 11.
A well-marked species, which I conceive to be generically
estranged from Gyrosigma hippocampa by the difference in
the curvature of the frustule, the arrangement of the striæ,
and the absence of the longitudinal furrow and central depression.
83. S P IIIN C T O C Y S T IS Hass.
Char. Frustules contracted in the centre; longitudinal furroio
and central depression absent ?
Derivation. From a-ffigtcTOS, constricted, and Kvani, a cell.
1. Sphinctocystis l ib e il is Hass.
Plate CII. Fig. 3.
Char. Frustules transversely striated, elongated. In front view
quadrangular, with straight sides and truncate extremities ;
in lateral aspect constricted in the centre with ohtuse ends.
Navicula lihrilis Abhandl. d. Akademie d. Wissensch. zu
Berlin, 1831, p. 81. 1833, p. 267. note. Frustulia
quinquepunctata Kützing, Linnæa, 1833, p. 554. t. xiv.
f. 28 .; Die Infus. p. 185. t. xiii. f. 21. Frustulia lihrilis
Jenner, in Fl. of Tunbridge Wells, p. 204.
Hab. Cheshunt: A. H .H . Aberdeen: Dr. Dichie. War-
burton, Lewes, &c. : Mr. Jenner.
A very curious species, which, on account of the centi’al
constriction and absence of the longitudinal furrow and central
depression, I have ventured to make the type of a distinct
genus.
Char. Frustules produced, longitudinally sulcated.
Derivation. From avXa^, a groove, and Kvaris, a cell.
1. A ulacocystis pellucida Hass.
Plate CII. Fig. 8.
Char. Frustules elongated, narrow, attenuated at each extremitg.
Navicula? pellucida. Die Infus. p. 176. t. xiii. fig. 3.
Frustulia pellucida Kütz., in Linnæa, 1833, p. 543.
t. xiii. fig. 11.; Jenner, in Fl. of Tunbridge Wells,
p. 204.
Hah. Ashdown Forest, and at Shoreham, Kent; between
Tunbridge Wells and the High Eocks : Mr. Jenner.
There can be no doubt of the propriety of separating this
species from the genus Navicula of Ehrenherg.
85. F E U S T U L IA Kütz.
Char. Frustules elongated, quadrangular, loith tioo longitudinal
grooves and two central depressions.
Derivation. Yxom. frustulum, a small fragment.
I must confess that I do not exactly understand the structure
of the single species which I propose to retain in the
genus Frustulia. It is possible that to this genus should be
referred those species of Navicula which have striated frustules
; and, if not to this genus, possibly those species should
be regarded as Cymhellæ.
1. F r u st u l ia ? viridis
Plate CII. Fig. 2.
Char. Frustules large, elongated. In front view quadrangular,
with straight sides and truncate extremities ; laterally
slightly inflated in the centre, loith rounded ends.
r F 3