M
M!
owing to their deeper constriction, the central position of their keel,
and their less firmly siliceous structure. They are frequently found
in large numbers, and with the exception of one species are marine in
their habitat. They are common in the estuaries of all our larger
rivers, and the sheltered bays of the southern and western coasts of
England. I have also examined specimens from the coast of Normandy,
the shores of the United States, and the Arctic Regions.
1 . Amphiprora alata, Kiitz. P. twisted; F .V . elliptical, with
rounded extremities ; V. linear-elliptical ; keel accompanied by a
double line of puncta; surface of V. striated; striæ 42 in ‘001".
Length -0025" to -0052". v.v.
Kiitz. Bacill. hi. 63. Bright. Inf. x. 1.3. Frit. Anim. xvi. 5 & 7. Bail.
Obs. 8, 9, 10.
Marine and brackish water : very common. Coast of Sussex, April and
Aug. 1850, W. Sm.
Plate XV. 124. Frustnle with endochrome. Frontispiece, fig. CXXIV.
2. Amphiprora paludosa, n. sp. F. twisted ; F. V. elliptical, with
round or truncate extremities ; constriction very deep ; V. striated ;
striæ 60 in -OOl". Length -0016" to ‘0042". v.v.
In fresh or slightly brackish water. Near Lewes, Sept. 1852, W. Sm.
Supp. Plate XXXI. 269.
3. Amphiprora didyma, n. sp. F. straight, elliptical, deeply constricted;
striæ faint, 73 in '001". v.v.
Marine. Lytham, Lancashire, Sept. 1849, W. Sm.
Plate XV. 125.
4. Amphiprora vitrea, n. sp. F. straight ; F. V. elliptical, constriction
very slight; V. lanceolate, striated; striæ 52 in -OOl".
Length -0023" to -0052". v.v.
Marine. Shoreham Harbour, Sept. 1852, W. Sm.
Supp. Plate XXXI. 270.
5. Amphiprora constricta, Ehr. F. membranaceous, hyaline,
straight, elliptical ; V. linear-elliptical, with a central sinus and
transverse line ; striæ faint, 68 in 'OOl". Length ’0024" to •0054".
v.v.
Kiitz. Bacill. xxix. 34. Prit. Anim. xvi. 6 ?
Marine and brackish water. Coast of Sussex, April 1850, W. Sm.
Plate XV. 126.
G e n u s 1 8 . AMPHIPLEURA, Kütz.
Frustules free, linear; V. with longitudinal ridges.
The structure of the present genus is somewhat obscure. I have
not been able to detect the nature of the ridges so conspicuous on
the front view, nor to determine the parts of the valve from which
they project. Ehrenberg, in his great work lufusionsthierchen, taf. xiii.
fig. iii. 7, gives an ideal section of the frustule, which represents the
ridges as springing from the surface of a convex valve, having between
them a depression which corresponds in position with the ordinary
median line of the Navicula. I am unable to confirm this description,
although I have on frequent occasions examined the living and dry
valves.
Frustules 1. Amphipleura pellucida, Kütz. linear-lanceolate.
Length -0033" to •0054". v.v.
Kiitz. Bacill. iii. 52. Aulacocystispellucida, Hass. Alg. cii. 8. Nav. pellucida,
Ehr. Inf. xiii. 3. Prit. Anim. iii. 140. xvi. 1.
Fresh water. Lewes, Nov. 1850, TF. Sm.
1851, Mr. G. Smith.
Plate XV. 127.
Katefield, Lancashire, Jan.
2. Amphipleura sigmoidea, TV. Sm. Frustules sigmoid. Length
•0058" to -0138". v.v.
Amphipleura rigida, [Kiitz. Bacill. iv. 30. ad specim. authen. quæ communicavit
cl. De Brebisson.
Marine and brackish water : forms a distinct pellicle or stratum. Bexhill,
Sussex, Sept. 1850, TF. Sm. Lancing, Nov. 19, 1852.