as that author gives EcMnella obtusa of Lyng. Tent. Ixix. F., and Fritstulia
obtusa of Ag. Consp. p. -14, as synonyms of his species. Dr. Greville’s
Herbarium, containing original specimens of Lynghye’s and Agardli’s species,
which are identical, enables me to state that that species is different from the
present, and hi fact belongs to the genus Diatoma, tlie zigzag arrangement of
the frustules being perfectly distinct, and the side view of the valve being
slightly constricted near the extremities and inflated in the middle, precisely
as may be seen in occasional specimens of Diatoma elongatum. If entitled to
rank as distinct, Lynghye’s specimen must be placed near that species, and
take tlie name of Diatoma obtusum. Kützing’s figure of Denticula obtusa
accords so nearly with the present, that I am disposed to think that lie had
our species before him, and must leave the reference to stand with a mark of
doubt until the examination of an actual specimen enables me to determine
the point. If the figure given hy Rabenhorst be original, it would confirm the
view here given, as it accords exactly with my species, and not at all with
Frustulia obtusa, Ag., which is given as its synonym.
Plate XXXIV. 292.
2 . Denticula tenuis, Kütz. Frustules linear, truncate; V. lanceolate,
acute; striæ 40 in -OOl"; costæ about 12 in -OOl". Length
of frustule -0006" to ‘0015". v.v.
Kiitz. Bacill. xvii. 8 ? Denticula acuta, Raben. Siissw. Diat. i. 7 ?
Fresh water. Plumpton, Sussex, April 1852. Larne, July 1853, W. Sm.
Lancaster, Nov. 1853, Mr. Johnson. Mountains, Forfarshire, Dr. Dickie.
Isle of Arran, Dr. Arnott. (Fountain at Nismes, May 1854, W. Sm.)
A small and more acute form than the last, but doubtfully distinct.
Plate XXXIV. 293.
3. Denticula inflata, n. sp. Frustules linear, or elliptical; V. oval,
with rounded, or acute extremities; striæ 40 in -OOi"; costæ
about 12 in -001". Length of frustule -0005" to -0007". v.v.
Fresh water. Beachey Head, Sussex, Aug. 1852, W. Sm. (Château d’Eau,
Montpellier, and Fountain at Nismes, May 1854, TF. Sm.)
The smaller size and broader valve alone distinguish this species from the
last two, with which it may be necessary eventually to unite it.
Plate XXXIV. 294.
4. Denticula ocellata, n. sp. Frustule linear, truncate, with conspicuous
foramina on F. V. ; valve linear, elliptical ; striæ 40 in
•001"; costæ 10 in-OOI". Length of frustule •OOOS" to •OOl l". v.s.
Fresh water. Near St. Abb’s Head, July 1855, Dr. Balfour.
I had the pleasure of detecting the above species during the printing of tlie
present sheets, in a gathering sent me by Dr. Gregory of Edinburgh. The
frustules on the F. V. closely resemble small specimens of Fphithemia Argus,
but the valve is wholly difl'ereiit. The extremities of the costæ or canaliculi
appear as circular foramina on the F. V., and the costæ on the S. V. also
give an ocellated appearance to the valve, which serves to distinguish it from
any other species in the present genus.
5. D e n tic u la s in u a ta , n. sp. Frustule linear, truncate ; V. lanceolate,
margin with three undulations; striæ delicate, 52 in •OOl";
costæ interrupted, 10 in -OOl". Length of frustule -0008" to
•0015". v.v.
“ Denticula sinuata,” ad specimiua sub hoc nomine quæ misit am. Thwaites,
Oct. 4, 1848.
Fresh water. Near Bristol, Mr. Thwaites. Wray, Nov. 1851, Mr. Geo.
Smith. Killiecrankie, Mr. P. Grant. Dryburgh, March ; Pentland Hills,
July 1854, Dr. Greville. Cumbrae Island, Feb. 1854, Mr. R. Ilennedy.
Plate XXXIV. 295.
G en u s 35. F R A G IL A R IA , Lyng.
Frustules linear, straight, united into a filament, free or attached,
direct ; valves linear, or elliptical, direct, striated.
The filaments of the present genus are less fragile than those of
any previously described, and in this respect the name, as I have
elsewhere remarked, has been unfortunately retained for species
which had better have been ranged under another appellation. In
fact, nothing can be more embarrassing than the changes to which
the various species originally described by Lyngbye under the name
of Fragilaria have been forced to undergo. Only one of the eight
species he has placed in this genus will be found below, and that one
has been restored to its position in opposition to the authority of
Professor Kützing, who has excluded it altogether from the Diatomaceæ.
I t must be admitted that the species described by Lyngbye are
far too heterogeneous in their characters to be united under one
genus, and that their separation was imperative in the present more
advanced state of the science ; still it is much to be regretted that