WALKER-ARNOTT, ON ARACHNOIDISCUS. 161 
In Smith’s ‘Synopsis of British Diatomacezx,’ p. 25, the 
genus Arachnoidiscus is said to have been proposed by Bailey. 
But I have before me the following extract of a letter from 
Dr. Bailey, of date July 27th, 1853 :—“I see that Smith, in 
his ‘ Brit. Diat.,’ gives me as the founder of the genus. This 
is not correct, but the species is mine, and it is very different 
from the A. Japonicus with which Smith confounds it.” The 
founder of the genus was Mr. H. Deane, of Clapham, and it 
was first noticed in a paper read by him before the Micro- 
scopical Society on 17th March, 1847. This paper was not 
published, and although it contained a general description of 
the disk, no distinguishing character was given. Mr. Shad- 
bolt, on 14th November, 1849, read a paper “On the Struc- 
ture of the Siliceous Lorica of the genus Arachnoidiscus,”’ 
and confirmed the generic appellation. In Pritchard’s ‘ In- 
fusoria,’ 2d. ed. (1852), the generic character will be found, 
and there also the name is correctly ascribed to Mr. Deane. 
In the ‘ Micrographical Dictionary’ it is said that Ehrenberg 
had now withdrawn the name Hemiptychus, as there was 
already a Hemipticha, a genus of Hemipterous insects. 
I now come to the species. In Pritchard’s ‘ Infusoria,’ 
page 700, the species there figured is called A. Japonicus of 
Shadbolt. Now Shadbolt’s specimens (figured im the ‘ Micr. 
Soc. Trans.,’ 11.) were from South Africa, and (if there be 
really more than one species) are not the same as the Japan 
form, and consequently not entitled to that name. Then 
again Bailey, as already said, gave the name of A. Ehren- 
bergi to a species from California (Puget Sound), which he 
supposed to be quite distinct from ‘A. Japonicus.”’ I cannot 
find that Bailey ever published this species; but Smith, in 
his ‘ Brit. Diat.,’ adopted it on the authority of De Brébisson, 
quoting A. Japonicus of Pritchard as a synonym. It 1s not 
very clear to me which Dr. Bailey meant. I have examined 
a slide prepared in 1853 from the Puget Sound form (got off 
an alga), and find it identical with the Japan one, but not 
with what is figured by Shadbolt or Pritchard; and another 
prepared by the late Professor Smith, and marked by him as 
obtained by Professor Bailey from California, and sent on 
22d October, 1856: but this is the African form figured by 
Shadbolt ; so that, if there be no mistake on the part of Dr. 
Bailey or Professor Smith, Dr. Bailey at first called the 
Japan form A. Ehrenbergii, and afterwards applied that name 
to the “A. Japonicus, Shadb.,” or African form. ~Smith has 
certainly not shown his usual sagacity in the elucidation of 
this genus; his generic character is nearly the same as Shad- 
bolt’s and Pritchard’s, but does not apply to the figure given 
