416 PROCEEDINGS OF SOCIETIES. 
tervals into irregularly-shaped forms, increasing in size from 
within outwards. 
Lejeunia hamatifolia exhibited.—Dr. More showed examples of 
Lejeunia hamatifolia, forming with its delicate structure a very 
pretty low-power object, and an interesting member of the Irish 
Cryptogamic Flora, as indicative of the average mildness of the 
climate. 
Navicula undulata, n. s., O'Meara, distinguished from N. 
distans.—Rey. EK. O’Meara exhibited a very interesting form of 
Navicula, which he regarded as hitherto undescribed, and of 
which the characters are as follow:—Median line undulate; 
striz broadly costate, not reaching the median line; cost in the 
middle remote, very short, those next somewhat longer, much 
closer, and finer towards the ends. This form much resembles 
NV. distans, but differs from it inasmuch as the median line in the 
present case is obviously undulate; the cost, too, are closer, 
and the ends broader than in that species; length 0:0056" ; 
breadth 0:0013”. Mr. O’Meara proposed to name this form 
Navicula undulata. It was found on seaweeds collected many 
years since at the Giants’ Causeway. 
On some seemingly novel or undescribed points of structure in 
Ballia callitricha, var—Mr. Archer drew attention to certain 
points of structure in a species of Balla, Harvey (Ballia calli- 
tricha, var.), seemingly not recorded in the descriptive works. 
The chief of these was the presence of pits at either end of the 
joints of the principal rachides, and of more than two, but 
smaller, in certain other of the cells of the frond, each of these 
pits covered or closed up by a lenticular, hemispherical, or kettle- 
drum-shaped lid or stopper. Both in its bearing on this alga, and 
as an example of a peculiar kind of secondary deposit (?) in a 
vegetable cell, this structure would seem to have a considerable 
amount of interest. Another feature, not shown in the books, 
was the apparent, but only apparent, introversion of the upper 
ends of the joints (more striking in those of the principal 
rachides) to receive a seeming conical projection of the lower 
ends of the upper joints. As first suggested by Professor E. 
Perceval Wright, the state of affairs, however, is quite the reverse. 
The lower ends of the joints are each laterally cleft or sub- 
divided, and curved off in front lke a “bishop’s mitre,” to receive 
the tapered and laterally wedge-shaped end of the lower joint. 
The joints of the rachides are not cylindrical, but narrowed 
upwards with a sigmoid curve at each side, a character likewise 
not noticed in the books. Filling each of the spaces thus pro- 
duced there is an intermediate peculiarly- figured cell (these Mr. 
Archer would denominate “ ramification cells”) not shown in the 
books, from which cells take origin not only the ordinary branches, 
by a complicated formation of preliminary septa, but also from the 
ultimate subsidiary cells produced therefrom are given off the 
first cells of a cortical stratum, from which latter, afterwards, 
emanate, after a peculiar fashion, those curious collateral fila- 
