420 Mr. C. Mereschkowsky on Okedenia, Hul. 
divisions, although fine, can easily be seen even without an 
oil-immersion *. 
This fact is of great importance, as it shows once more 
that O. scopulorum and O. inflewa are very nearly allied 
forms. They have both very narrow elongated valves, with 
distant terminal nodules ; the striz in both are nearly of the 
same kind, the zone in both is complex, and last, but not 
least, the endochrome in both is almost the same. There can 
be no doubt, therefore, that they belong to one and the same 
genus. And since O. scopulorum cannot, on account of its 
endochrome (not to mention other characters), be a Navicula, 
neither is it possible to place it in the genus Amphora; 
therefore O. inflewa, being so nearly related to O. scopulorum, 
can neither be regarded as belonging to the genus Amphora. 
So it becomes necessary, as an inevitable conclusion, to 
establish a separate genus, the name of which cannot be 
otherwise than Okedenia, as it has already been applied to 
one of these species. 
Okedenia pontica, Mer. (PI. VII. figs. 17-19.) 
Mereschkowsky, Diat. d. 1. m. Noire. 
‘There are but few differences between this species and the 
preceding one if only dead shells are taken into consideration ; 
the size is smaller, being about 0°075 mm. in length, the 
girdle-face is broader, but the endochrome is very different ; 
the number of chromatophores is eight, which is as constant 
in this species as the number four is in O. inflewa. The 
form of the chromatophores also differs in some respects 
from those of the latter species, the horns are not so elongated 
and they are undulated instead of being straight. ‘The two 
inner pairs of chromatophores are usually nearer to each other 
than to the outer pairs. Hach pair of opposite chromato- 
phores are united by a common central spherical pyrenoid 
(fig. 18). 
I have observed this species by hundreds in the Medi- 
terranean (Villefranche), and always with exactly the same 
structure of their cell-contents. 
When the diatom is not in a very fresh condition the horns 
begin to contract and the plates take the appearance shown in 
fig. 19. 
The zone is complex, as in O. inflexa. 
* I have seen these divisions, as represented in fig. 3, on unmounted 
specimens observed in water with Hartnack’s objective IX. (water- 
immersion), 
