Mr. C. Mereschkowsky on Stauronella. 429 
By no means. The structure of the frustule is opposed to 
such a conclusion. And, further, there are other groups of 
the Raphidian diatoms which are equally characterized by 
a transverse disposition of their two chromatophore-plates. 
Such is the case, for instance, with certain Amphiprore. It 
is generally admitted that Amphiprora has a single chroma- 
tophore *; but here, again, my researches have shown that 
this is not quite so. It is true that A. paludosa has a single 
chromatophore-plate, but in several other species I have found 
two plates—a superior and an inferior—separated in the 
middle by a transverse interval, exactly as in Netzschia. 
Stauronella constricta cannot, however, as already mentioned, 
take its place in the genus Amphiprora, its raphe being 
straight and not sigmoid as in that genus. We come there- 
fore to the inevitable conclusion that this diatom belongs 
to a new genus—Stawronella—nearly allied to Amphiprora, 
and forming with the latter a transitional group between the 
Raphidez and Carinate f. It represents, in my opinion, a 
remnant of a very old, now almost extinct, group of diatoms, 
which I propose to call Archaidex. ‘This is a central group 
from which have sprung on one side the Raphidian Diatoms 
and on the other the Carinate (Nitzschiex, Surirelloidee). 
As remnants of this group or as living representatives of the 
Archaidexw I consider the genera Stauwronella, Amphiprora, 
Amphoropsis {, Aurtcula, and Epithemia. This theory will 
be explained more completely in a paper now in course of 
publication. 
* Cleve, Syn. of the Navic. Diat. part i. p. 18. 
+ In my paper “ Sur la Classification des Diatomées ” (Scripta Botanica, 
St. Petersburg, fasc. xviii.) I have established a new system of classi- 
fication of the Diatoms, in which I divide them first in two groups—the 
Mobiles, provided with a slit or a series of holes in the walls of the 
frustule, and therefore being endowed with movement; and the Immobiles, 
without such a structure, and therefore unmovable. The Mobiles are 
again divided in two groups—the Raphidiez in the generally accepted 
sense, and the Carinatw, comprising the Nitzschioideee and Surirelloides. 
The Immobile diatoms are also divided in two groups—the Bacilloidez, 
including the Pseudoraphidiez with the exclusion of the Carinate; and 
the Anaraphidiez in its old acceptance. I hope that this system, which 
has the advantage of doing away with the highly artificial group Pseudo- 
raphidiew, will be generally accepted by diatomists as being at the same 
time simple and very natural. 
{ Under the name of Amphoropsis I unite forms with a straight raphe 
elevated on a keel turned in the same direction, with asymmetrical valves 
and with two chromatophores disposed transversely, or with granules. 
The following species belong to this genus :—A. recta ( Tropidoneis recta), 
A, conserta (Trop. conserta), A. pontica, sp. n., A. stauroners, Mer., and 
probably A. Van Heurcku (Trop. Van Heurckit). 
