Okeden^ on Diatomacece. 
87 
exactly in all their other characters. The smaller form 
alluded to by Dr. Arnott appears to have been considered a 
young state of C. Hodgsonii by Professor Smith ; but as in 
addition to the difference of structure already alluded to, I 
never remember to have seen any valves of an intermediate 
size, that could serve as connecting lines between them, and 
though both may be considered among our rarer British 
species, the smaller one is by far the most abundant, I am 
inclined to concur in the propriety of giving it a distinct spe- 
cific name. 
On the DiATOMACE^ of South Wales. 
By FiTZMAURiCE Okeden, C.E. 
(Read June 16th, 1858.) 
Having read the remarks made in his address by our late 
president as to the paucity of slides contributed to the cabinet 
of the Society, I must confess that I feel the justice of them, 
and the more so as, if I mistake not, the subject has been 
alluded to by a former president in his address. I have, 
therefore, ventured to come forward to assist in removing 
that reproach which our late president considered as resting 
upon the members from the smallness of their contributions. 
During the last five years, while resident at Haverfordwest, 
in Pembrokeshire, I have employed my leisure hours in 
studying the Diatomaceae of the country. 
The town itself is situated on the banks of a tidal river, 
overlooking extensive salt marshes, which are frequently over- 
flowed by spring-tides, and abounding in shallow pools and 
ditches ; not far from it are some large and quiet fish ponds. 
A few miles to the north, at a place called Churchland, is a 
large tract of boggy land, at the foot of a mountainous dis- 
trict; mill-streams, over-falls, and weirs, so favorable to 
Diatomaceous growth, abound in the neighbourhood y while 
near to Carmarthen is a vast and extensive morass, inter- 
sected by ditches, and excavated into pools by the turf-cut- 
ters. And lastly, there are the shores of Milford Haven, 
and the extensive mud-banks of the tidal estuary of Neyland, 
which latter I have penetrated by boring to a depth of 
twenty, thirty, and forty feet, and succeeded in obtaining 
many interesting species at these depths. 
The result of a five-years exploration of all these localities 
has been the collection of upwards of fifty genera, including 
