ill!Ill

i54
MASTOGLOIA.
A. Valves with strice not interrupted by sulci or hyaline spaces
making together the figure of a lyre.
1. Valve lanceolate with loculi arranged in an arcuate row.
M. Smithii Thwaites. (W.Sm., S.B.D., ii., p. 65, pi. 54, f. 341,
H.V.H. AtL, pi. 4, f. 13* ; Type No. 46), plate 2, fig. 60.
Valves elliptical with apices often slightly produced, rostrate ; marginal
plates broad ; attenuate at the apices ; showing
from 6 to 8 loculi, central
nodule slightly extended laterally ; striae robust, distinctly punctate, radiant
up to the extremity of the valves, 15 to 17 in 1 c.d.m. Length, 3 to 4-5
c. d. m .
Fresh and brackish water. Bergh, Brabant (Delogne), Antwerp (P.G.), Blankenberghe
Kitton), Ireland (O'Meara, West).
(H.V.H.). England (W. Sm. !
Var. lacustris Grun. (H.V.H. AtL, pi. 4, f. 14* ; Type No. 47),
plate 2, fig. 61.
Differs from the type form by being narrower and by the nodule
being much more extended laterally.
Mixed with the type form at Bergh.
M. apiculata W. Sm. !
plate 25, fig. 700.
(s.b.d. ii., p. 65, pi. 62, f. 387*),
Valves oval or lanceolate-elliptical, with apices apiculate, obtuse. Loculi
narrow, very numerous, varying from 30 to 50, and arranged in a regular arc,
which occupies nearly the entire outline of the valve ; stria; transverse,
distinctly punctate, radiant, up to apices of the valves, about 15 in 1 c.d.m.
Length of valve 4 to 7 c.d.m. ; breadth, 1*5 to 2 c.d.m.
Brackish water. Shores of England (W. Sm. !), Ireland (O'Meara), Norway, France, etc.
Will probably also be found in Belgium.
M. lanceolata Thwaites. (w. Sm., s.b.d. i., pi. 54, f. 340 ;
N. Meleagris Kittz. H.V.H. Atl., pi. 4, f. 15, 16, 17*), plate 2, fig.
62.
Valves lanceolate, infinitesimally attenuate up to the sub-obtuse apices ;
loculi generally numerous ; nodule not extended laterally ; stria; about 20 in
1 c.d.m., slightly radiant nearly up the apices, where they become convergent.
Length, about 5 c.d.m.
Brackish water. Not yet found in Belgium. England, Ireland, Holland, Denmark, Sweden.