58 
Roper, on Triceratium Arcticum. 
of an inch : his figures and description are_, however, sufficient 
to identify the species. 
In October, 1853, Professors W. H. Harvey and J. W. 
Bailey, in describing some species of Diatomacese adhering to 
or entangled in algae, brought home by the United States^ 
Exploring Expedition under Captain Wilkes, U.S.N., have 
described a species as Triceratium Wilkesii, from Puget^s 
Sound,"^ and also a form under the name of Amphitetras 
TVilkesii, which has been found with most of the known 
gatherings of the Triceratium, and is now generally considered 
a four-sided variety of the same species. 
I am not aware that any of the original gathering of this 
species has been sent to this country ; but Dr. Arnott informs 
me that some logs of wood were imported into Liverpool some 
little time back from Puget^s Sound, attached to which were 
some zostera leaves and small zoophytes, and from a boiling 
made of them were obtained both triangular and square forms, 
which agree with the descriptions given by Prof. Harvey and 
Bailey, and show that these species are clearly identical with 
that previously described by Mr. Brightwell as T. Arcticum. 
It foUows from this, that the Triceratium Wilkesii and 
Amphitetras TVilkesii of Harvey and Bailey must be cancelled 
altogether, and the name of Arcticum be retained, to include 
the species from both localities on the ground of priority. 
The species from Vancouver's Island is identical in structure 
with the preceding forms, and though the figures given by 
Mr. Brightwell in '^Mic. Jour.,' vol. i, t. iv, fig. 11a and d, 
are sufficiently characteristic, I give rather a fuller specific 
character to assist identification for the future. 
Triceratium Arcticum, Brightwell. 
Valves, with slightly convex or straight sides, with small 
but distinct areolations, radiating in lines from the centre, 
and becoming very minute at the angles, which are obtusely 
rounded, and slightly enlarged ; connecting membrane with 
similar reticulations to the valve, arranged in transverse lines. 
Diam. -0105 to -0054 of an inch. Syn. Tri. Wilkesii H and B. 
Var .j3. Four angles. Syn. Amphitetras Wilkesii, H and B. 
Marine, Beechey Island, Arctic Begions; Puget's Sound; 
Vancouver's Island; and in a fossil state at Monterey Bay. 
Triceratium Montereyii, though. somewhat similar in struc- 
ture to Arcticum, is readily distinguished, from having an 
elevation or boss on the centre of the valve. 
T. condecorum difi^ers in the absence of the minute reti- 
culations at the angles, and T. striolatum from the angles 
being produced into horn-like processes. 
* ' Mic. Jour,/ vol. iii, p. 94. 
