302 Proceedings of the Royal Irish Academy. 
phyt., p. 84. This last synonym is given on the authority of Heiberg, 
who had the opportunity of inspecting authentic specimens. 
Cork Harbour, Wm. Smith. Rock-pool, Salt Hill, Co. Dublin. 
Coast of Galway, from collections by M‘Calla, in the Herbarium, 
Trinity College, Dublin. 
Genus VY. Scnizonrma, Agardh. 
Frond usually much divided. Frustules arranged in one or more 
files within the gelatinous tubes which constitute the frond. 
Smith remarks justly that ‘‘ the fronds in this extensive genus 
were amongst the earliest Diatomaceous organisms recognised by 
naturalists, and have been the perplexity of all subsequent observers.” 
Nor is this to be wondered at, when the difficulties attendant on their 
examination are taken into consideration. The frustules enveloped 
in the fronds are generally minute, so that even though they were 
free it would be no easy matter to examine them satisfactorily, and 
the difficulty is much enhanced by the intervention of the fronds as 
well as by the manner in which the frustules are packed within them. 
Kiitzing attempted to arrange the species on the basis of the charac- 
ters of the fronds, but with how httle success the student will be 
convinced who endeavours to make himself master of the subject by 
the aid of his minute descriptions, and of his very indefinite figures. 
Heiberg falls into a mistake the very opposite to that of Kiitzing— 
discarding from consideration not only the characters of the fronds in 
the various species, but regarding the fact of the frustules being normally 
incased within fronds as an unreliable generic distinction, and so he 
ranks the species under the genus Navicula. De Breébisson had ob- 
served that ‘‘the greater part of the species needed reconsideration, 
and to be studied with regard to the character of the frustules.’’ and 
Smith, with his characteristic sagacity, taking this hint, at the same 
time not overlooking any reliable character exhibited by the fronds, 
dispelled the confusion which had hitherto existed, and reduced the 
species into an order, which seems, all the circumstances considered, to 
admit of little improvement. 
As to the mode of reproducing the sporangia in the genus, opinions 
differ, as the following extract from Pfitzer will sufficiently show :— 
‘‘In Schizonema Grevyillii, according to Smith, a single mother-cell 
produces a single auxospore, while according to Liiders this occurs 
but seldom, namely, when one auxospore becomes defunct ; usually, on 
the contrary, two cells co-operate, and form two auxospores. The 
development of the latter occurs outside the tubes in a large and fine 
mucous investment. The mode of proceeding, according to Liiders, is 
that each mother-cell divides itself, and the halves unite in pairs. 
However, in other forms in which, according to Liders, a similar 
