Roper, on the DiatomacecB of the Thames. 73 
And in the Mud from Nev)haven Earhour. 
Actinocyclus senarius Pinnularia peregrina 
Coscinodisciis eccentricus ,, didyma 
Gallionella sulcata Khaphoneis rhombus 
Grammatophora marina 
A proof of the widelj-extended distribution of these species. 
From the first of the foregoing lists 1 have selected a few 
species for more particular notice, and annex drawings of the 
most interesting, on the scale adopted by Mr. Smith, namely, 
400 diameters. 
There is a large species of Coccorieis (PI. VI. fig. 1), elliptical 
in form, and marked longitudinally with undulating striae, and 
also with faint transverse lines, concentric with the extremities 
of the valve, but only visible with a high power and oblique 
light. The perfectly elliptic form and peculiarity of the cross 
striae seem to distinguish it from the C. placentula of Mr. 
Smith ; but I am doubtful whether it may not be a variety of 
that species. 
Of the four species of Eupodiscus, the most plentiful is 
E. 7'adiatus, which, from one specimen, in which three frustules 
were conjoined, may probably sometimes occur concatenated, 
in a similar way to Odontella aurita. E. sculptus, the most 
peculiar in its markings, is rarely met with ; and E. fulvus 
and argus are sparingly distributed. The latter shows the 
delicate hexagonal reticulations alluded to by Professor Quekett 
as marking the Tripodiscus Rogersii of Professor Bailey. The 
star-shaped cells appear, when seen by direct light, to be 
placed in the centre of small bosses or protuberances, in which 
it differs from all other DiatomacecB that I am acquainted with. 
The Actinocyclus undulatus of Mr. Smith's Synopsis occurs 
abundantly. This species appears to include the Acti- 
noptychus senarius of Ehrenberg and Kiitzing ; but after a 
careful examination of many specimens, I have been unable 
to make out any undulations similar to those of fig. 4, in 
Plate V. of the Synopsis, in the large species that occur in the 
Thames and elsewhere ; and although a multiplication of 
species is a point carefully to be avoided without good 
grounds, it appears to me that the appellation undulatus 
should be confined to a small form, in which these undula- 
tions distinctly occur, and the large and well-known species 
retain the name originally applied to it by M. Ehrenberg, 
namely, A. senarius. 
Sparingly distributed, I have another large and beautiful 
disc (fig. 2), with sixteen septa, the surface of which is covered 
with faint cross striae, similar to those of Pleurosigma ; and in 
* See Histological Catalogue, p. 212. 
