Mr. C. Mereschkowsky on Stauronella. 431 
The valve of the type species is never linear, as described 
by some authors, but always considerably attenuated towards 
the ends; the latter are invariably truncate, the middle part 
being more or less constricted, with a few exceptions amongst 
small individuals (fig. 6). The form of the valve is very 
constant, the only variation consisting in its greater or less 
breadth: fig. 5 represents a narrow form, the valve being 
more linear ; fig. 2 is more typical. 
The girdle-face is very badly reproduced by A. Schmidt 
(Atl. xxvi. fig. 37) as well as by Peragallo (D. m. d. Fr. 
pl. vi. fig. 32); both figures represent it in an oblique 
position, and give no idea whatever of its real appearance. 
This is due to the fact that the diatom under consideration 
has, it appears, never been studied on raw material, as it 
ought to be, but only on mounted specimens in slides, from 
which it usually disappears during the cleaning of the 
material. I have seen hundreds, perhaps thousands, of 
frustules, and fig. 1 (Pl. VIII.) represents a typical specimen 
of it; fig. 4 is also good. Sometimes two frustules are united 
by their sides, as in fig. 8, and such cases show a striking 
resemblance to Ehrenberg’s figure*. This removes all 
doubt as to the identity of Stawroneis constricta of Ehrenberg 
with the form here described. 
The outlines of the frustule are strong and coarse, the 
constriction in the middle always well marked ; the stauros 
appears as a very bright round bead. The extremities are 
more (figs. 3,4) or less (fig. 1) narrowed, the ends being 
roundly truncate, more distinctly truncate when the frustule 
is broad (fig. 4). The zone is very finely but distinctly 
striate in a longitudinal direction, the strie or divisions (5-6 
in number) never terminating in marginal puncta as in var. 
linearis. 
I give here a series of individual measurements, which show 
that the size is far from being so large as stated by Cleve 
(0°05-0'14 mm.), who was evidently in possession of some 
variety. 
Breadth of At the 
Length. the frustule. constriction. 
mm. mm. mm. 
0-021 eeshis Leer 
0-025 0:0076 0:0057 
0-0266 0-0095 0-0086 
0:0266 0:0095 eer. 
0:0285 0:0086 0:0067 
* IT have not seen the original figure, but only its reproduction in 
Wolle’s ‘ Diat. of America.’ 
