ill!Ill

442
MELOSIRA.
M. Jurgensii Ag. (Syst. Alg., p. 9 ; M. subflexilis IV. Sm.; H.V.H.
Atl., pi. 86, f. 1-3 and 5* ; Type No. 460), plate 18, fig. 612.
Differs from the preceding by its more elongated frustules and its valves
more convex, and very constricted near the margins.
Brackish water. Belgium, Holland, England, Germany, etc. ; Scotland (Kitton in Baxter
Coll., No. 3846).
var. octogona Grun. !
460), plate 18, fig. 613.
Connecting zone with blunted angles.
(H.V.H.
Atl., pi. 86, f. 9*; in Type No.
Brackish water. Austruweel near Antwerp. Mixed with the type-form.
** Junction surfaces of frustules plane, often denticulate.
I. FRUSTULES SHOWING A SULCUS AT THE SUTURAL MARGIN.
M. Roeseana Rabenh. (Alg., Nos. 383 and 504, Sussw. Diat,
pi. 10; Oithosira spinusa //'. Sm. ; H.V.H. Atl, pi. 89, f. 1-6*; Type No.
465), plate 19, fig. 614.
Valves circular, with striae radiant, punctate, puncta becoming more and
more fine towards the centre, which is hyaline, and furnished with two to five
coarse granules; striae on the margin of the disc about 7 in 1 c.d m. Frus-
tules with valves constricted towards the disc, whose margins are denticulate,
and having near the sutural margin a broad and deep sulcus. Connecting
membrane very finely striate, about 21 striae in 1 c.d.m. Diameter of valve,
1 '25 to 4*5 c.d.m. Sporangial frustule almost spherical.
On moss, etc. Frahan (Delogne), France (De Brb. ), England (W. Sm.), Scotland (Kitton in
Baxter Coll., No. 3850), Ireland (O'Meara).
var. spiralis (Liparogyra spiralis Ehr. ; H.V.H. Atl., pi. 89, f. 7 and
8*; in Type No. 465), plate 19, fig. 616.
Frustules narrow and very elongated, furnished internally with a spiral
band transversely striate.
With the preceding. Very rare. Norwich, England (Kitton).
M. distans KlitZ. (Baa, p. 54, pi. 2, f. 12; H.V.H. Atl., pi. 86,
f. 21-23*; Type No - 46l )> plate 19, fig. 616.
Valve circular, with sparse, rather strong puncta. Frustules with very
thick valves, sulcus rather broad, but very deep. Striae, 14 in i c.d.m.
Fresh water. Hatrival (Del.). Found throughout Northern Europe.