WALLICH, ON TRICERATIUM. 251 
influence of the tides; and were found growing attached as 
a soft mossy stratum upon submerged Alew or tree stems. 
Been the beautiful jointed-looking filaments, I have desig- 
nated the eee by the name of Hi ydrosera. The characters 
are as follows 
Frustules attached, forming elongated direct filaments. 
Frustules either triangular prisms or compressed cylinders, 
attached to each other at each angle by a mucous cushion. 
Valve cellular, furnished with perfect septa; and, on one side 
only, with a remarkable series of aperture-like appendages. 
Connecting membrane quite plain; hyaline. 
Although the association of the triangular with the com- 
pressed form may, at first sight, appear untenable, the 
other characters common to both, and more especially the 
remarkable processes observable on one side only of each 
valve, appear conclusively to establish the fact of their ranking 
under the same genus. The two species I have named 
respectively H. triquetra and H. compressa. 
The specifie characters of the first are as follows: Frustule 
athree-sided prism, having a portion of each angle partitioned 
off by a septate process, which is partly given off from the 
inner wall of the valve itself, and partly, as in Rhabdonema 
‘and Mastogloia, from the connecting membrane. Valve 
triangular, sides undulated, surface reticulated. Angles 
rounde d, obtuse, and smooth, but furnished with two or three 
stout minute spines. On one side only of each valve, at the 
central portion of its outer margin, from two to five minute 
punctate appendages exist. Connecting membrane compound, 
its outer annulus exhibiting a continuation of the valvular 
septa, plain, annulate and undulate. Front view of frustule 
a parallelogram, rather longer than broad when not under- 
going division. F.V. length, from ‘0017 to ‘0050 Breadth, 
the same. KE.V. diamicter: the same. Cellulation from 
Sto Ldn 001.. 
The punctate appendages are visible also in F.V. on both 
valves on same side of the frustule; and in the filament, on 
the same side throughout. Around them the siliceous 
epidermis thickened. Free ends of the septa of valve 
hollowed out, the cusps resting on imperfect septate pro- 
cesses given off from the connecting membrane. The outer 
margin of the latter much thickened, and giving to the 
F.V. the appearance of a siliceous hcop encircling the margin 
of each valve. Connecting membrane, of two plates or hoops, 
during division, as mentioned in Tuceratium. The spines at 
the angles very minute, and requiring careful illumination, 
with a power of from 300 to 400 diameters, to bring them 
