i6o William J. Hodgetts. 
of this genus hitherto described, it has been looked upon as a new 
species. 
The filaments are quite unbranched, attaining a length upwards 
of 5 mm., and are usually fairly straight, and intertwined amongst 
other filamentous algae. The cells are cylindrical, with the excep¬ 
tion of the basal cell which is gradually attenuated (Pig. 2), and the 
apical cell, the tip of which is acuminate, and usually slightly swollen 
and curved, but never prolonged into a hair (Pigs. 1, 3, 4, 5). 
The possession of an acuminate apical cell is the chief feature 
which distinguishes the genus Uronema Lagerh. from Ulothyix, 
although the mode of attachment also appears to be different in 
the two genera, the filaments of Uronema being affixed dy a mucous 
cushion secreted from the extreme tip of the basal cell (Fig. 2), 
while those of many species of Ulothrix are attached by a simple or 
branched unicellular rhizoid. 
The cells vary in size between rather wide limits, being 4*4— 
9-6 (generally 5—7*5) fi wide, and 22—80 (generally 28—56) /x long, 
the length being 4—13 (usually 5—9) times greater than the width. 
There is rarely any variation in the normal cylindrical form—with 
the exception of the basal and apical cells—although a slight 
swelling in the middle part of cells about to divide, or which have 
just divided (Fig. 6), is rather general. The forms assumed by the 
apical cell are varied; those shown in Fig. 1, 3-5, represent the 
chief variations observed. A perfectly regular acuminate apex was 
rather uncommon, the most usual form being the slightly asym¬ 
metric and swollen apex shown in Fig. 4, although a more strongly 
curved and swollen, but always sharply acute, termination such as 
Fig. 3, was not rare. The cell-wall in the apical part of the terminas 
cell was sometimes slightly thickened but never markedly so. 
The basal cell (Fig. 1, 10) is always very gradually attenuated, 
and fixed to the subtratum by a small cushion of colourless 
mucilage, which apparently is a product of secretion of the cell, 
and is generally encrusted with much foreign matter, and some¬ 
times stained reddish-brown with compounds of iron. The cell-wall 
of the basal cell is usually somewhat thicker in the lower stalk-like 
part than elsewhere, and the narrow lumen here is filled with 
some hyaline pectic substance derived from the cell-wall, and 
probably the same as that of which the basal mucous cushion is 
composed. The latter may possibly be secreted through a minute 
terminal pore, but this point could not be definitely ascertained. 
The attachment of the filaments to the substratum is not very firm, 
