430 Mr. C. Mereschkowsky on Stauronella. 
The diagnosis of the genus Stauronella is as follows :— 
STAURONELLA, Mer. 
Valve narrow, linear or attenuated towards the ends, usually 
constricted in the middle; extremities truncate or rounded, 
rarely cuneate. Raphe straight, symmetric ; central nodule 
elongated transversely in a stauros. Gjirdle-face constricted, 
zone complex. Endochrome composed of two plates disposed 
transversely along one of the connecting-zones; each plate 
with a conspicuous pyrenoid. 
Contains one species, S. constricta (Ehr.), Mer., with 
several varieties. 
This diatom has not yet been sufficiently well described, 
and the figures, especially those of the girdle-face, are very 
unsatisfactory. I will therefore give here a good description 
of it, accompanied by figures, and then pass to the considera- 
tion of a new variety. 
Stauronella constricta (Ehr.), Mer. 
(Pl. VIII. figs. 1-6.) 
Stauroneis constricta, Ehrenberg, Amer. pl. i. 2, fig. 126; Peragallo, 
Diatomées mar. d. France, p. 56, pl. vii. figs. 32, 338. Stawronets 
(Libellus) constricta (Ehr.?), W. Sm., Cleve, Syn. Navic. Diat. 
part i. p. 145 (ex parte). Amphiprora constricta, W. Smith, Brit. 
Diat. i. pl. xv. fig. 126*. Stauronets amphoroides, Grun. (ex 
parte), A. Schm. Atlas, xxvi. figs. 37-39. ; 
Diagnosis.—Valve convex, narrow, linear-lanceolate, con- 
stricted in the middle, attenuated towards the extremities, 
which are broad, truncate. Central nodule extending trans- 
versely in a narrow stauros, reaching the margins. Strie 
25-27 in 0-01 mm. (Cleve), transverse. Axial area indistinct. 
Girdle-face narrow, constricted in the middle, where the 
stauros appears as a brilliant bead, narrowed towards the 
ends. Zone complex. Length 0-021-0°056 mm. (average 
0:04 mm.) ; breadth of valve 0°0052-0:0081 mm.; breadth 
of girdle-face 0°0076—-0°0105 mm., at the constriction 0-0057- 
0-0086 mm. 
Locality. North Sea (CZ) ?; Black Sea (Sebastopol, mar., 
Mer.) ; Mediterranean (Nice, mar., Per.). Fossil: Crimea, 
Kertch (sarmatische Stufe, mar., Mer.). 
* Not being in possession of the work of W. Smith, I am unable to 
say whether this quotation which I give after Cleve is correct or not. 
Cleve gives also as synonym the Navicula simulans of Donkin (Brit. Diat. 
p. 60, pl. ix. fig.3). But, as Van Heurck has shown (‘A Treatise on the 
Diatomacee,’ p. 235, pl. xxvii. fig. 784), this latter represents quite a 
different species. Whether it belongs to Stauwronella or not cannot be 
decided without knowing its endochrome; it is, however, not likely to be 
the case, as the girdle-face does not at all resemble that of S. constricta. 
