PYXIDICULA OPERCULATA. 21 
mistakes of others, nor his own, should now form 
the type of the preceding genus [Cyclotella] from this 
same species, prescribing the name at first proposed 
but altering the sense; and at the same time should 
describe, as a new species of Pywidicula, the P. oper- 
culata of Bailey, which seems either identical with 
that of Ehrenberg or very similar to it and to that 
so described and figured by the authors named above.” 
He adds his opinion that the specimens of Brébisson 
and Leonardi in his possession belong to Cyclotella 
and not to Pywidicula. It is evident that he believed 
Pyzidicula operculata to be the correct name for this 
species, and, had he not been merely annotating 
Fia. 166.—Pyzidicula operculata: a, vertical view ; b, side view, show- 
ing furrow by which the test separates, c, showing a transparent 
globular body ; d, a detached half. x 550. (After Pritchard.) 
Kuetzing’s memoir, ‘ Die kieselschaligen Bacillarien 
oder Diatomeen,’ he would have adopted that name. 
By all the above-named and some other writers— 
Pritchard, Brightwell, and Perty—this creature was 
considered to be a diatom. It was first determined 
to be a rhizopod by Carter, who found it in the island 
of Bombay, but he wrongly referred his specimens. 
to the Arcella patens of Claparéde and Lachmann. 
He says that it is very like Hhrenberg’s Pywidicula 
operculata, placed by him amongst the Diatomez. 
This appears to be his reason for rejecting it as a 
Pywidicula, and he adds that he thinks “ much alliance 
will be found to exist between the Rhizopoda and the 
Diatomaceex.”’ It was the opinion of Meneghini and 
some other naturalists that the diatoms were animals, 
and by Ehrenberg not only the diatoms but also the 
