ill!Ill

338
PLAGIOGRAMMA.
P. Gregorianum Grev. (Q.J.M.S., 1859, vii., p. 208, pi. 10,
and 2; H.V.H. Atl., pi. 36, f. 2*; in Type No. 104), plate 10, fig. 390.
Valve oblong lanceolate, with hyaline median portion showing an elongated
pseudo-ocellus, bordered with two robust costae, apices showing a large smooth
space. Striae 9 in 1 c.d.m., formed of coarse puncta, sub-quadrangular,
forming longitudinal lines ; girdle face quadrangular, obtuse. Length, about
2 to 4 c.d.m.
Marine. Blankenberghe. England (Stolt. ), Scotland (Greg. ), Ireland (O'M.), France (Breb. ),
Bahnsie (Lagerst), Denmark (Heiberg).
P. Van Heurckii Grun ! (h.v.h. Atl., pi. 36, f. 4 *), plate 10,
fig. 391.
Valve narrowly lanceolate, with apices generally somewhat rostrate capitate,
smooth, with a narrow hyaline transverse band bordered with two costae, far
from robust; strias 1 1 or 12 in 1 c.d.m., formed of small puncta, forming
longitudinal lines. Girdle face very slightly
f. 1
constricted from the middle to
underneath the apices, which are dilated truncate. Median portion only
showing one robust costae, formed by the nearness of the apex of the two
costae visible on the valve. Individuals united in rather long filaments.
Length, 1*5 to 4*5 c.d.m.
Marine. Found on one occasion on a jetty between Heyst and Blankenberghe, and at another
time in the mud sediment ot the second Basin at Blankenberghe. Surface of the River Dee,
England (Stolterfoth)
COHORT OF TABELLARIINE^.
ANALYSIS OF TRIBES.
f Frustules genuflexed ......Entopylese.
Frustules
not as
above.
( Valves pyriform (more or less in the shape of a pear) that is
cuneate-oval .....Licmopliorese.
f Frustules forming a spiral band .
Valves not /False septa very distinct, seldom
. Meridionese.
as above. "| Frustules J reduced to knobs . . TaPellariese.
not I
^
spiral. J
v False septa usually absent . DiatomeEe.
Tribe XL Entopyle^:.
Frustules showing rudimentary septa (diaphragms) ; valves furnished with
costee .......Entopyla.
Frustules without internal septa ; valves furnished with costae . . Gephyria.