1894. ] On Some Species of Micrasterias. 57 
first to notice the union into filaments.* Wolle found the fil- 
aments, and states? that the cells are held together by the 
overlapping of the end lobes. 
It is in connection with the form of this‘end lobe, and the 
means by which the cells are joined that the descriptions by 
various authors are most indefinite or confused. The figure 
in Ralfs’ British Desmidiee is very defective, and justifies 
Wallich’s remark that neither Bailey nor Ralfs seems to have 
noticed» the minute details of structure. Wallich describes 
the form which he found as var. B, but it seems scarcely dis- 
tinct from the type. He describes it as emarginate, with one 
spine on each surface, the two being diagonally opposite. 
He figures a chain of three cells, but they could not possibly 
be joined in the manner represented by him. 
Rabenhorst® mentions the species as one not yet found in 
Europe, and states that the emarginate polar lobe is biden- 
tate on each surface. Later writers seem to have followed 
him, and the statement is true, as far as it goes. The best 
figures of the terminal lobe are given by Nordstedt,® but 
there are some points not made clear by his plate and de- 
scription. 
The form of a single cell is shown by the accompanying 
drawing (figs. 2 and 3). The lateral margins of the frond 
are nearly straight and parallel, and the end lobe projects but 
slightly beyond them. This lobe is deeply emarginate, with 
an almost rectangular sinus. The portion on each side of the 
Sinus is depressed on one surface, in such a way that the two 
depressions lie diagonally opposite each other. This is very 
difficult to describe, but may be easily understood by refer- 
ence to the drawings. At the base of the sinus on either sur- 
face of the frond are two tooth-like projections. These have 
been often noticed before, but one peculiarity seems to have 
been overlooked. The tooth on the side adjoining the de- 
Pression is nearly twice as large as the other. An examina- 
tion of hundreds of specimens shows this to be constant. 
The manner in which the cells are joined in the filament 
ra be seen from fig. 4. The lower cell is slightly separated 
ti m the next, showing the manner in which the lateral por- 
“ons of the end lobes of the two fronds are dovetailed to- 
*Loc. cit. 
uit of the United States, 118. 
. ora Europaea Algarum aquz dulcis et submarine. 3: 195. 1868. 
