416 Mr. C. Mereschkowsky on Okedenia, ul. 
of the frustule or the valve as of that of their cell-contents 
that I find it necessary to separate these forms from their 
respective genera and to unite them in one new, or, rather, 
revived genus. The chromatophores of Amphora inflera and 
Navicula scopulorum are, indeed, so peculiar and so different 
from those of MNavicula and Amphora, that it seems very 
unnatural to unite them with either of these genera; and at 
the same time the endochrome is so similar in both that there 
can be no doubt as to their near relationship. 
Besides the two above-mentioned diatoms, I include in the 
same genus Okedenia two new forms which are characterized 
by their endochrome. ‘The endochrome being thus the main 
characteristic, as well of the genus as of the species which it 
includes, I will now proceed to its description. 
Okedenia scopulorum (Bréb.), Mer. 
(Pl. VII. figs. 1-3.) 
Navicula scopulorum, Bréb. in Kiitz. Spec. Ale. p. 81; Grunow, Ver- 
handl. 1860, p. 547, pl. i. fig. 6; Donkin, Brit. Diat. p. 73, pl. xii. 
fie. 5; Cleve, Syn. Navic. Diat. part i. p. 151; Peragallo, Diat. mar. 
d. Fr. p. 68, pl. viii. fig. 26. Pimnularia Johnsonn, W. Smith, Br. 
Diat. pl. xix. fig. 179 (1853). Navieula Johnsonii, Van Heurck, Syn. 
D. d. Belg. p. 99, Suppl. B, fig. 28. 
The endochrome consists of 16-38 granules or little plates 
regularly disposed in pairs along both of the connecting- 
zones. Hach plate is composed of two narrow longitudinal 
bands, occupying respectively the right and left side of the 
frustule, and connected in the middle by a narrow trans- 
verse bar, thus reproducing exactly the letter H. When 
seen from the valve-face they appear as simple sticks disposed 
in two rows along both sides of the valve (fig. 1). It is 
only when the frustule takes an oblique position that both 
opposite plates with their eight prolongations can be seen 
simultaneously. 
In some cases the transverse band may be broader than is 
represented in fig. 2; but such cases are not typical. The 
terminal chromatophores reach the extremities of the frustule, 
in the middle they are not more distant than elsewhere. The 
central part of each chromatophore contains a pyrenoid, which 
has the shape of a flat disk or ellipsoid, appearing more or 
less rounded when seen from the girdle-face and more elon- 
gated elliptic when seen in profile, 7. e. from the valve- 
face. When the diatom is dead the H-formed plates become 
contracted, and they appear then as simple round granules 
(Pl. VII. fig. 4, and woodcut figs. 1, 2). 
