Sect. IA^. Pseudo-nodule obsolete ; frustule straight.
21. Synedra crystallina, Kutz. V. much elongated, slightly inflated
at the centre and extremities; striæ reaching across the
valve, 26 in -OOl". Length -0180" to -0266". v.v.
Kûtz. Bacill. xri. 1. Diatoma crystallinum, Ag. Consp. p! 52. et Grev. B. F.
p. 407. ad specim. authen. quæ communicavit cl. Dr. Greville.
Marine. Poole Bay, Sept. 1851, W. Sm.
Plate XII. 101.
22. Synedra superba, Kütz. V. linear, slightly attenuated from
the centre towards the rounded extremities ; striæ very distinct,
27 in -001", reaching across the valve ; pedicel somewhat elongated.
Length of frustule -0098" to -020S". v.v.
Kiitz. Bacill. XV. 13.
Marine. Poole Bay, Nov. 1849, WC Sm.
Plate XII. 102.
23. SynedraGallionii, Ehr. V. attenuate, extremities obtuse; striæ
not reaching across the valve, 36 in -OOl"; pedicel not elongated.
Length of frustule -0060" to •0112". v.v,
ji. A shorter and stouter form.
Ehr. Inf. xvii. 2. Kiitz. Bacill. xxx. 42.
Marine. Isle of Man, Mr. Johnson. ¡3. Beachy Head, Aug. 1852, W. Sm.
Supp. Plate XXX. 265. Var. (3. Supp. PL XXX. 265 ¡3.
24. Synedra fulgens, W. Sm. V. slightly inflated at the centre and
at the rounded extremities ; striæ reaching across the valve, 36 in
•001"; frustules arranged in a flabellate manner upon a branched
pedicel. Length -0068" to -0164". v.v.
Exilaria fnlgens, Grev. S. C. F. pi. 291. Ucmophora fulgens, Kiitz. Bacill.
xin. 5. ad spec, authen. quæ misit amicus De Brebisson, Jan. 1853
rrit. Amm. xvi. 20.
Marine. Poole Bay, Sept. 1851 ; Jersey, Aug. 1852, W.Sm.
Plate XII. 103.
There is nothing in the structure of the frustule to warrant the separation
of this species from the present genus.
B R I T IS H D IA T O M A C EÆ . 75
G e n u s 2 4 . COCCONEMA, Ehr.
Frustules stipitate, cymbiform; valve with a submedian line, having
nodules at centre and extremities.
The frustules of this genus differ in no respect from those of Cymbella
(Genus 3), and are placed apart solely from the presence of a
stipes. AVhether the development of this accessory be esteemed a
generic difference or not, it cannot be denied that it gives a notable
physiognomy to the plant, and affords a ready means of discrimination.
The stipes seems to be an exudation from the frustule,
secreted only during the progress of self-division. I t assumes, in the
present and other genera, a membranous consistency and filamentous
form; while the same secretion is present in Cymbella and many of
the free Diatomaceous forms as a mucous stratum, and in others as a
gelatinous cushion or prolonged pedicel.
AVhere it possesses a filamentous character it invariably branches
in a dichotomous manner,—a necessary consequence of the self-division
of the frustules, and the circumstance that each filament or branch is
the secretion of a separate frustule. Thus, when self-division is com-
pleted, the extension of the filament below the frustules is suspended,
a joint or articulation is formed at the base of the dividing frustule,
and each of the half-new frustules begins anew, in its progress towards
special self-division, the secretion of a new joint or internode; and a
dichotomy is the result. Conjugation and the formation of Sporangia
m the present genus have been observed by Mr. Thwaites in C. lan-
ceolatum and C. Cistula, and by myself in both these species and
C. parvum.
I. Cocconema lanceolatum, Ehr. F.V. lanceolate, obtuse; AA elongated,
slightly inflated at the centre of the concave margin ; striæ
moniliform, 21 in -001". Length -0043" to -0058". v.v.
(3. Much elongated (Sporangial ?). Length -OOSS"’ to -0098".
Ehr. Inf. xix. 6. Kiitz. Bacill. vi. 3. Dujar. Inf. xx. 4. Prit. Anim. iv. 195.
Ilass. Alg. ci. 1. In Conjugation, Thw. Aim. vol. xx. pi. xxii. C.'
Fresh water: frequent. In Conj. River Froome, Dorsetshire, Mar. 1847.
Coekshiit stream near Lewes, Ap. 1850. Plumpton, Sussex, Ap. 1852, W. Sm.