202 WALKER-ARNOTT, ON ARACHNOIDISCUS, ETC. 
Evunorra.—To define this genus appears to have caused 
Professor Smith some trouble; at first his intention seems to 
have been chiefly to distinguish it from Epithemia, with which 
it was combined by Ehrenberg; but in his second volume, 
under Himantidium, he proposes to introduce the radiating 
strize as a character. One of his species (£. arcus) may be 
left out of consideration, as this grows attached to small 
algze, by the end, by means of a “ cushion-like pedicel,” as in 
Synedra, to which genus it belongs; indeed, when I met with 
it,im that state, near Brodick, in Arran (July 1854), it was 
so closely intermingled with S. pulchella and S. gracilis that 
I then felt disposed to consider it a deformity of one of these. 
In all the genuine species of Hunotia which I have examined 
previous to or after a very slight maceration in acid, I find 
the portion called the valve by Smith to be more composite 
than can be inferred from his figures, each being made up of 
parallel slices or lamina, easily observed in the F. V.; and I 
have been so unfortunate as never to see the connecting zone 
as represented: indeed, had Mr. West’s accuracy not been 
beyond suspicion, I should say, as the result of my own 
observations on recent gatherings, that this broad zone did 
not exist, and that the supposed single valve was composed 
of several valves, each separated by a very slender and almost 
invisible zone. I therefore, at present, consider each sup- 
posed valve to be formed of a series of frustules, and that the 
connecting zone figured in Smith’s work is some accidental 
enlargement of one of the slender connecting zones. Be 
that as it may, the divisibility of the supposed valve into 
several is perfectly different from what has been seen in the 
genus Himantidium, where the valves are incapable of dividing 
and are separated by a siliceous zone of considerable breadth. 
This structure at once enables us to remove &. gracilis, Sm., 
(although the frustules are often solitary) to Himantidium, 
under which genus the small state of it had been previously 
described by Kutzing as H. exiguum of De Brébisson. 
Ampnora.—Some friends having expressed a wish that I 
should explain my views of the structure of the genus 
Amphora more fully than given at p. 184 of this volume of 
the ‘ Micr. Journ.,’ I subjoin the following extract from the 
paper as originally prepared. 
Kutzing’s ideas of the structure of this genus are not 
very clear. If we compare his description of it with that of 
Navicula, and swppose that in the former he has mistaken the 
Front for the Side view of the frustule, the characters of both 
will scarcely differ, and his views would thus be much the same 
