252 WALLICH, ON TRICERATIUM. 
out clearly. They are probably of use in strengthening the - 
mucous cushion whereby the angles are held together; the 
filaments being remarkably tenacious. Frequently composed 
of from thirty to forty frustules. 
The frustules vary greatly in size, but never in general 
contour, although the sides are at times more inflated than 
at others. The side exhibiting the punctate processes being 
generally the most convex. In lke manner the angles are 
sometimes acute, sometimes subacute; an angular bend 
existing in the end view, where the septa coalesce with the 
margin. Cellular structure thickest at centre of valve, and 
varying to a limited extent in coarseness, although always 
large and easily seen in this species. Under a power of 200 
diameters, the marking seems minutely cellular; but ampli- 
fied to 400 diameters, it is shown to consist of a number of 
large reticulated polygonal spaces, having a tendency to the 
hexagonal character, and divided by narrow lines or ribs, 
which coalesce with each other. Entire frustule perfectly 
siliceous. Endochrome equally distributed, granular, and of a 
pale but rich green. 
In H. compressa the characters are : 
Frustule, a compressed cylinder, forming lengthened fila- 
ments, as in H. ¢triguetra. Valve elliptical, sides undulated. 
Angles subacute. Valve in E.V. divided into three compart- 
ments by two septa thrown across it. Angles smooth and 
occasionally exhibiting two or three very minute spines, as in 
the former species. ‘The punctate appendages on one side 
only. Connecting band plain, annulate, undulate, imdefi- 
nite. F.V. as in H. triqueira, a parallelogram, with subacute 
angles. 
In the front view the three compartments are inflated ; the 
central one being the largest. Ends full, rounded, and hyaline, 
with no trace of cellulation. 
F.V. Length of frustule, ‘0017 to 0048; breadth, :0017 
to ‘0048. §.V. length, from ‘0017 to :0048; breadth, -0006 
to ‘0014. E.V. length, from -0017 to ‘0048. Breadth of 
central compartment, ‘0017 to ‘0084. Breadth of terminal 
compartment, ‘00086 to ‘0014. ; 
It is difficult to suggest, with any approach to certainty, 
the purposes subserved by the unsymmetrically placed lateral 
processes alluded to. But, in all probability, they are ana- 
logues of the central and terminal nodules of other diatoms. 
On a future occasion, I hope to offer some remarks on the 
peculiarity they present, and to poimt out more particularly 
their resemblance to the unsymmetrically placed puncta in 
Gomphonema geminatum, and in two new Indian species of 
