constricted near both extremities ; the upper slightly produced,
linear and truncate ; the lower somewhat capitate and obtuse ;
striæ 20 in -001". Length -0012" to -0017". Greatest breadth of
V. -0003". v.s.
Greg. Mic. Jouni. vol. 4. pl, i. 42.
Fresh water. Lough Leven, September 1854, Dr. Gregory.
69. Gomphonema insigne, Gi-eg. V. lanceolate, upper extremity
rounded, lower subacute ; striæ 20 in -OOl". Length of F. -0016"
to -0025". Greatest breadth of V. '0005". v.s.
Greg. llic. Journ. vol. 4. pl. i. 39.
Fresh water. Duddingston Lough near Edinburgh, April 1854, Dr. Greville.
Braemar, August 1854, Dr. Balfour.
The last two species are probably varieties of the same form.
70. Gomphonema Fibula, Bréb. F. V. slightly cuneate; V. sub-
linear, constricted near the upper and larger extremity, which is
conspicuously capitate, obtuse at the lower; stipes abbreviated;
nodule obsolete ; striæ 40 in -001". Length of F. -0016" to -0024".'
Greatest breadth of V. '00025". v.v.
Bre'b. in Kiitz. Sp. Alg. p. 65. ad specim. authen.
, Eackham Common, Sussex, August 1853, W. Sm. (Falaise
M. De Brebisson.) ^ ’
The absence of a nodule aud the abbreviated stipes would rather point to
Synedra as the genus of this form ; but the cuneate frustule is precisely that
of a Gomphonema.
71. Gomphonema subtile, Ehr. Valve slightly inflated at centre,
gradually attenuated towards both extremities, the upper of which
is capitate and truncate, and the lower obtuse ; striæ 26 in -001".
Length of F. -0018". v.v.
^^'■yol^4^7l “ • Mic. Journ.
Fresh water. Lough Avaul, Co. Cork, June 1855, W. Sm.
Doubtfully distinct from G. constrictum or G. acuminatum. First detected
as a British form by Dr. Gregory of Edinburgh, and said by him to occur in
two localities in Scotland.
PODOCYSTIS, Bail. Nov. Gen.
Frustules attached, sessile, cuneate ; valves convex, obovate, striated ;
with a median line and transverse costæ.
The transverse costæ or canaliculi distinguish this genus from
Podosphenia; its attached growth and moniliform striæ from Surirella.
72. Podocystis Americana, Bail. Striæ moniliform, 30 in -001";
costæ 12 i n -001". Length of F . -0016" t o '0026". Greatest breadth
of V.-OOll". v.v.
Bail. Mic. Org. fig. 38. Doryphora elegans, Roper, Mic. Journ. vol. ii. p. 284.
Marine. In the mud of Fembroke Harbour, August 1854, Mr. Roper.
(NewYork, on Grinnellia Americana; communicated by Dr. Arnott. Near
Marseilles, May 1854, W. Sm.)
B.
The follow'ing list includes those British forms described or figured
by other writers, wliich are either unknown to me, imperfectly known,
or appear to belong to species included in Vol. I. of the present
Work
Epithemia gibbemla, Ehr., Greg. Mic. Journ. vol. 2. pl. iv. 2.
Eunotia incisa, Greg. Mic. Journ. vol. 2. pl. iv. 4. v.s.
This appears to be a new species ; but, not haiiug seen it iu a fresh state,
I am unable with certainty to determine either its generic or specific characters.
It will probably be found to be a Himantidium. Its valves are arcuate,
rounded or subacute at tlieir extremities, with suhterminal notches or depressions
oil their concave mavgius ; striæ 44 in '001". Length 'OOlfi" to 'OOSJ".
Eunotia F alx, Greg. Mic. Trans, vol. ii. p. 105 ; Mic, Journ. vol. 3.
pl. iv. 1 = Synedra Hemicyclus, Ehr, in Kiitz. Sp. Alg. p. 48. Ehr.
Microg. pl. xvi. i. 38 & xvi. ii. 47.
Cymbella truncata, Greg. Mic. Journ. vol. 3. pl. iv. 3 = C. affinis,
W. Sm. Synopsis, pl. xxx. 250. v.s.