110 
present such manifold transitions, as well in respect to the ap- 
pearance of the striation as to the outline of the form, that in 
most cases it is difficult to decide whether the specimen should 
be referred to one or the other.” The correctness of this remark 
is obvious to all careful observers, but still the species seem to be 
distinct. 
The following characters seem to distinguish Mavicula viridis 
from NV. major : The costz are finer and less radiate ; the median 
free space is narrower and less expanded around the central 
nodule, and the normal outline is linear-elliptical.— O'Meara. 
NAVICULA PUSILLA, W. Sm. - 
Navicula pusilla, Sm., Syn., Vol.i., p. 52, pl. XVII., fig. 145; Ralfs in Prit. 
Infus., p. 900; Donkin, Brit. Diats., p. 20, pl. IIl., figs. 6a and 6b.; Brun., p- 75, 
pl. VIL., fig. 36b; Van Heurck, Syn. Diat. Belg., pl. X1., fig. 17; O’Meara, Rep. 
on the Irish Diat., p. 381, pl. 32, fig. 14; Rabenh., E. Diat., p. 193. 
Navicula gastroides, Greg. 
Navicula tumida, var. subsalsa, Grunow. 
Valve small, broadly oval with produced short truncate ends ; 
striz distinct, moniliform and reaching to the median line, con- 
vergent opposite the central nodule and radiate towards the apices. 
Haé.—Brackish water, scarce. Salt Meadows at New — 
(Plate LXIX., fig. 2.) 
Prof. Gregory distinguished his Navicula gastroides from this 
species by its stouter habit and larger size; but we unite them, 
as Prof. Smith has done, being unwilling to add another doubt- 
ful species to this group, which we believe is already too numer- 
ous.—Ralfs. 
NAVICULA OBLONGA, Kiitz. 
Navicula oblonga, Kiitz., Bacill., p. 97, t. 1V., fig. 21; Ralfs in Prit. Infus., p. 
907; O’Meara, Rep. on the Irish Diat., p. 344, pl. 30, fig. 10; Van Heurck, Syn. 
Diat. Belg., pl. VII., fig. 1. 
Pinnularia oblonga, Brun., p. 82, pl. VIIL, fig. 3; Sm., Syn., Vol. i., p. 55, Pl 
XVIIL., fig. 165; Rabenh., Siissw. Diat., p. 45, t. VI., fig. 6. 
Navicula macilenta, Ehr., Infus., 1838, t. XXI., fig. 13. 
Pinnularia macilenta, Ehr., 1844. 
Pinnularia polyptera, Ehr. 1844. 
Valve elliptical linear, with broad, rounded extremities, 
cost stout, convergent at the centre, and radiate towards the 
ends ; intermediate free space narrow, but roundly expanded at 
central nodule. 
