74 Roper, on the Diatomacece of the Thames. 
that respect it resembles the valves from Natal, for which 
Mr. Shadbolt proposed the name of Actinophoenia ; but I find 
this striation is no distinctive character, as all the specimens 
of A. undulatus (or senarius) that I have examined have the 
same peculiarity, and the septa are plainly discernible, espe- 
cially with the parabolic condenser. In the lists I have ap- 
plied to it provisionally the name of Actinocyclus sedenarius, 
as it approaches very nearly to Ehrenberg's figure of that 
species in the 'Berlin Transactions' for 1839, tab. 4, p. 2. 
The septa appear to have their origin from the smooth central 
portion or pseudo-nodule, and to terminate at slight eleva- 
tions or openings at the margin of the disc, and in perfect 
specimens those on one valve are opposite to the interspaces 
on the other. The front view exhibits slight traces of undu- 
lations, as in fig. 13, not in continuous waved lines, but rising 
to points at the extremities of the rays, giving the side view 
an appearance similar to that of a ridge-and-furrow roof. The 
diameter varies from l-288th to l-187th of an inch. 
Of the genus Triceratium four species occur. A small one, 
by no means uncommon, is represented by fig. 3, which 
I ; consider the T. striolatum of Ehrenberg ; it has convex 
sides, small horn-like processes at the angles, which are rather 
obtuse, and is marked with minute dots or cells, radiating 
from the centre. In the determination of this species I am, 
after a careful examination, compelled to differ from Mr. 
Brightwell, who, in his monograph of this genus in a late 
Number of the ' Microscopical Journal,' refers to a Paper by 
M. Ehrenberg in the ' Berlin Transactions ' for 1839, in which 
there is a figure of T. striolatum^ and the following description 
of the species: — " Testulae lateribus triquetris convexis, angulis 
sub-acutis, superficie subtilissime punctato-lineata, dorsi cin- 
gulo maedio laevi ;" and yet Mr. Brightwell describes it as 
with " concave ends," and figures it with concave sides ; and 
in the frustules I have seen of his species, the central band on 
the front view is punctate or cellular, whereas it is described 
by Ehrenberg as smooth. The cellular structure of the side 
view is also so plainly apparent, that it would hardly have 
been described as " subtilissime punctato-lineata " by so careful 
an observer. Looking, therefore, at Ehrenberg's figure and 
description, I should conclude that the species figured by 
Mr. Brightwell cannot be the T. striolatum, but should re- 
ceive some other appellation. The concave sides would seem 
to refer it to T. pileus of Ehrenberg ; but I have not seen a 
figure or full description of that species. 
Triceratium alternans of Bailey is rarely met with ; and I 
have only one specimen of T. undulatum, in which the peculiar 
