Mr. C. Mereschkowsky on Okedenia, Hud. 421 
Okedenia granulata, Mer. (PI. VII. figs. 12-16.) 
This species could hardly be distinguished at all from the 
preceding but for the endochrome, which is again quite 
different from that of all other species of this genus, having in 
common only the great number of chromatophores. These 
latter differ both in form and in their disposition. Their form 
is rounded, somewhat dilated transversely, without any trace 
of prolongations or horns (figs. 12, 14) ; there exist not even 
the concavities at their margins, as in O. scopulorum, var. 
fasciculata. They are usually eight in number, although 
they sometimes attain to eleven (fig. 16). The most im- 
portant characteristic of this species consists, however, in 
the disposition of the granules. In all forms hitherto 
examined the chromatophores have been seen resting with 
their median line on the connecting-zone (see figs. 2, 7, 11); 
here they are always placed on the surface of the valves, 
with their margins alone resting on the zone (fig. 13). 
Usually they are situated at regular distances, each chroma- 
tophore of one valve being opposite that on the other valve 
(fig. 13); in a few rare cases I have found them to have an 
irregular disposition, as shown in fig. 16. When the diatom 
is dead the granules leave the surface of the valves and 
become scattered in the middle part of the frustule (fig. 15). 
This position of the granules on the surface of the valves 
constitutes a character of such importance that the above- 
described form cannot be considered otherwise than a distinct 
species. It differs also in some respect by the frustule and 
the valve; the size is smaller, varying from 0:0456 to 0:057 
mm.; the valve is less arcuate, the ventral margin being 
almost straight (figs. 12, 14), and the median line also seems 
to be almost straight * ; breadth of the valve 0-0052-0-0057 
mm., breadth of the girdle-face 0:0095-0:0U11 mm. Zone 
complex. 
I have observed two dozen living specimens of this species 
in the Pacifie Ocean (San Pedro, California), usually in 
Plankton material. 
And now if we again refer to the Plate and compare the 
different figures (especially figs. 2, 7, 11, 12, 17) repre- 
senting the endochrome of all these forms, we can easily see 
how closely allied they are in this respect, constituting, no 
doubt, a very uniform and natural group. And the form of 
* T have not yet had an opportunity of examining mounted specimens 
of this species. 
