O’Mrara—Report on the Irish Diatomacee. 315 
rately. One can, however, satisfy himself that the diaphragms are 
open at one end, by observing a perfect frustule in transverse view, 
when one diaphragm is seen from the open, and the other from the 
closed, side.’”,-—De Danske Diat., p. 72. In the case of the diaphragms 
of Striatella, it may be noticed that the silicious plate is thicker at 
one end, and becomes gradually thinner as it recedes from it. This 
fact may serve to illustrate the mode of growth in the diaphragms in 
other species, as well as in Striatella. Springing from opposite ends, 
the two contiguous diaphragms in some cases appear much thicker at 
the starting point, and as they proceed parallel to each other become 
thinner and thinner as they approach the opposite end of the frustule. 
The strong lines which appear as coste on the front view may seem to 
mark the extreme length to which the diaphragms project into the cell ; 
but the compressed rings are, except in the case of Striatella, com- 
plete, and can by proper focusing be traced through their entire 
course. 
Genus I. Grammaropnora, (Ehr.) 
Frustules attached, united in zig-zag filaments ; diaphragms two in 
number; open in the centre, and equally developed at both sides of 
the same. Valves narrow, elliptical; sometimes slightly expanded in 
the middle; strize obvious, and appearing on front view as a narrow 
striate border. 
Although the species of this genus are by the experienced eye 
easily discriminated, it is not easy to describe their characteristics 
in words so as satisfactorily to obviate confusion with other forms 
belonging to the same family, especially with Tabellaria, which they 
resemble, not only in the mode of growth in zig-zag filaments, but 
also in the general formation of the diaphragms, which are equally 
developed on both sides of the central portion. Whether we view the 
frustules on the front or side views, they may be distinguished by the 
following characters:—In Grammatophora the valves are sometimes 
slightly expanded in the middle, but in no case so much so as in Tabel- 
laria; the striw, too, are ever noticeable, which is not the case with 
the last-named genus. And on the front view the narrow margin of 
strize noticeable in the species of Grammatophora are never to be seen 
in those of Tabellaria. 
Grammatophora marina, (Lyngb.) Marine. 
Frustules on front view regularly quadrangular; on side view 
narrow, elliptical; striz obvious; diaphragms curved near the ends, 
and thence running in a straight line towards the middle. (Pl. 29, 
me), 
e ren Bac., p. 128, T. xvii., fig. 24, who regards the species as 
identical with Diatoma marina, Lyngb. Wm. Sm., B. D., Vol. i1., 
R.I.A. PROC., SER. II., VOL, Il., SCIENCE. » 
