NELLIE CARTER! FRESHWATER ALGÆ. 55 
glistening pearls under the low power of the microscope. As regards its 
systematic position, it seems nearest to Hapalosiphon, differing chiefly in the 
absence of heterocysts, its irregular branching, and in the usual absence of 
the thin, firm sheath commonly present in that genus. Its branching is 
sparse and irregular, the branches arising in all directions, and branches of 
the second order being quite frequent. The branches make practically a 
right angle with the parent branch, and all the cells, both of the main axis 
and the branches, are similar to each other, becoming simply more slencer 
towards the apex. The alga has striking characters which distinguish it 
from ail others. It has a peculiar form of apical growth by the budding of 
the apical cell, and the continued growth of this small portion budded off 
until it is large enough to be cut off as a distinct cell (Pl. 4. figs. 4, 5). 
Very rarely a gelatinous sheath is present, or it may be represented by an 
almost invisible difHuent colourless mucus surrounding the filaments. 
Sometimes it apparently becomes firm and yellowish, and in this condition it 
often has a peculiar radiating structure which recalls the structure of the 
mucous sheath in certain filamentous Desmids (Pl. 4. fig. 6). The absence 
of heterocysts is peculiar, and in view of the fact that the significance of 
these cells is still not properly understood, it is noteworthy that the alga 
associated with Rosaria ramosa, namely Mastigocoleus obtusus, was also desti- 
tute of heterocysts, although in the other species of the genus Mastigocoleus 
heterocysts are present. 
FISCHERELLA AMBIGUA (Nüg.) Gom. Specimen without locality. 90. 
Europe, India, Sandwich Islands, America. 
STIGONEMA HORMOIDES (Kütz.) Born. et Fla. Specimen without locality. 
1092. Europe, Australia, America. 
STIGONEMA sp. crass. fil. sine teg. 30 p; cum teg. 60 u ; diam. cell. 8 u. 
Plaine des Lacs ; in shallow rain pools. 338. The filaments were not 
infrequent; they were about 1 mm. in length, unbranched, and were 
probably in an imperfect state of development. 
RIVULARIACE AE. 
RivuLARIA Hamarires (DC.) Ag. Pic La, inerusting rocks in trickle of 
water. 864. Europe, America. 
BACILLARIEZ. 
MELOSIRACEÆ. 
Mevosira ITALICA Kütz. Mont Humboldt; with Blue-green algæ on 
stones in rock pools. 1045 a. 
