Mr. C. Mereschkowsky on Okedenia, Zul. 419 
that of O. scopulorum. The chromatophores are of the same 
H-like shape, composed of two elongated bands united in the 
middle by a short transverse part (fig. 11), but they are much 
more elongated and always four in number; the middle part 
contains in its centre an elongated pyreneid, which, however, 
here is confounded with the pyrenoid of the opposite plate, 
so that each pair of plates contain only one common pyrenoid 
(fig. 9). Cases where pyrenoids of two opposite plates are 
united into one are not unfrequent among diatoms; I have 
observed them in Mastogloia Braunti, Gr., M. pumila, Grun., 
Amphora ostrearia, Bréb., A. lineolata, Ehr., Achnanthidium 
brevipes (Ag.), Cl., A. glabrata, Grun., Hantzschia amphioxys 
(Ehr.), Gr., Licmophora flabellata (Carm.), Ag., &c.; it also 
exists in some species of Synedra and Fragilaria (F. hyalina 
(Kz.), Gr., for instance). 
The four plates with all their prolongations can be simul- 
taneously seen only when the frustule takes an oblique 
position as represented in figure 10. 
The only difference between the two species consists in the 
number of plates, of which there exist here only four, and, as 
a consequence, they are of greater length. 
I have observed hundreds of living specimens of this species 
both in the Black Sea (Ialta, Crimea) and in the Mediter- 
ranean (Villefranche), and they all had a similarly con- 
structed endochrome and the number of the chromatophores 
was invariably four *. 
Okedenia inflexa may be regarded as an asymmetrical form 
of O. scopulorum, the more so as the valve of the latter shows 
sometimes a marked asymmetry in its general form, but 
especially in the disposition of the raphe ft. The form and 
structure of the frustule and of the valve of these two species, 
as well as their endochrome, thus points to their close affinity. 
It is true that the zone of OU. anflexa is complex, while it is 
said to be simple in O. scopulorum, and Cleve places the 
latter in his subgenus Microstigma, characterized by a simple 
zone}. But this is a mere supposition, not based on direct 
observation of the frustules of the species. In reality O. scopu- 
lorum has a complex zone (fig. 3), and the longitudinal 
* By the way, this diatom is certainly not an exclusively pelagic form, as 
is generally believed, although it sometimes occurs in pelagic gatherings ; 
but I have usually found it, sometimes in great abundance, living at a 
depth of 4-10 metres among thin green Cladophora-like alge. Okedenia 
pontica, Mer., lives under the same conditions. 
+ See Peragallo, Diat. mar. d. France, pl. viii. fig. 29. The valve 
itself in this figure is somewhat Reeenetrical 
t Cleve, Synops. of the Nay. Diat. part i. p. 142. 2 
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