Roper, on the Diatomacece of the Thames. 75 
projection of the posterior valve beyond the undulating sides 
of the upper, as noticed by Mr. Brightwell in his Paper before 
alluded to, is plainly shown. 
Campylodiscus costatus and crihrosus are frequently met 
with. Another small species is represented by fig. 4, which 
Mr. Smith informs me he has named hi-costaius^ and that he 
will give a figure of it in the addenda to his second volume. 
In appearance it so much resembles C. clypeus, that I had 
applied that name to it, especially as that species is included 
in Ehrenberg's lists as occurring at Gliickstadt, Hamburg, and 
some localities in Holland, and was found by Professor Bailey 
in Lake Monroe. The valve is nearly circular, saddle-shaped, 
canaliculi about forty, distinct, length at the sides about half 
the radius, at the ends much shorter. The central portion 
has two narrow bands of costcB parallel with the terminations 
of the side canaliculi. Diameter is about 1 -384th of an 
inch. 
The most abundant species in all the slides I have examined 
is represented by figs. 7 to 10, which I believe would all 
be included as varieties of Doryphora amphiceros by Mr. 
Smith, and as different species of Rhaphoneis by Ehrenberg 
and Kiitzing. The difference of form is so great, and the 
peculiarity of the cellular markings so apparent, that they 
appear to furnish data for specific distinction quite as good 
as are afforded in many species of Navicula and Plenrosigma. 
Not having Ehrenberg's figures or descriptions to refer to, 
T am guided solely by the species Algarum " of Professor 
Kiitzing. Fig. 7, from its lanceolate form, strong granular 
markings, and well-marked median line, might probably be 
referred to Rhaphoneis gemmifera. The length varies from 
l-319th to l-320th of an inch ; breadth, about l-1090th of an 
inch : it occurs but sparingly. Fig. 8 is rarely met with, but 
is readily distinguished by its more robust form, the greater 
delicacy of its striae, and the slightly marked and nearly 
parallel sides of its median line. The length is l-349th of 
an inch, and breadth l-779th of an inch. It would be referred 
to Rhaphoneis fasciolata. Fig. 9 is exceedingly common, and 
in the size of its markings resembles fig. 7, but differs in 
being more concentric, and nearly obliterating the median 
line at the acute extremities of the valve. The breadth of 
the valve is also much greater in proportion to the length. 
The length is l-600th of an inch, and breadth l-1224th of 
an inch. It agrees with Rhaphoneis pretiosa. Fig. 10 is 
widely different from any of the preceding, and is by no 
means abundant. The valves are very diaphanous, the mark- 
ings faint, median line obscure, and form sub-orbicular, the 
