RECENT RESEARCHES IN THE DIATOMACE®. 205 
ecurs in Neidium, 
parallel to the longitudinal axis. In this genus two mother-cells produce 
two auxospores. 
Stauroneis (Ehren.).—This genus is distinguished from Navicula by the 
transversely-expanded middle nodule, but corresponds with it in the dis- 
position of the cell contents. Before the cell-division, there occurs a move- 
ment of the endochrome plates, which are often deeply constricted, and 
sometimes even interrupted in the middle. Stauroneis pheenicenteron has 
been seen in copulation, and in this case, as observed by Archer, two 
mother-cells produced but one auxospore. 
instructa,” (Flor. Europ. Alg. sect. 1, p. 258) 
Pfitzer adds the peculiar unstriated border, somewhat analogous, as he says, 
th the thickening of the walls occurring in the parenchyma of the leaves of 
e Pine. 
In the structure of the primordial cell, P. acutum and P. legumen, the 
only species of the genus, correspond with Navicula. A central kernel is 
observable. The condition of the endochrome plates in the process of 
of its valves, ts its inner structure is closely allied to Navicula. 
In the freshwater species P attenuatum (Keitz.), P. acuminatum (Kütz. 
and Grunow) — tre, W. Sm. (our author says, P. Spencerii, W. Sm., 
rupted by the interposition of frequent laeunz. Long before the division 
takes place in the case of the freshwater forms of Pleurosigma, the endo- 
: ; t 
the 
plasma takes place. Auxospores have not yet been found in the genus 
Pleurosigma. 
Frustulia. Supposing the peculiarities of this group to be so marked 
as to justify the separation of the forms comprehended in it from the genus 
Navicula, and the establishment of a new genus to receive them, the name 
lefined, Süssw. Diat. p. 50, 
lines interrupted in the middle without central nodule, nestling in a gela- 
