294 Proceedings of the Royal Irish Academy. 
Genus VIII. Rwarnoners, Ehr. 
The characters on which this genus is grounded are :—First. The 
symmetry of the frustules by which they are separated from Cocconeis, 
which some of the species in other respects closely resemble. Secondly. 
They do not form parallel filaments, by which circumstance they are 
distinguished from those of Denticula and Dimeregramma. Thirdly. 
The striz are interrupted by the interposition of an unstriate longi- 
tudinal band, more or less broad—a feature by which the forms of the 
genus may be discriminated from those of Diatoma and Odontidium. 
While adopting this genus, I do so with somewhat of the feeling 
which Grunow has so well expressed in the following remarks :— 
‘(The genus Rhaphoneis, which here I represent in Ehrenberg’s 
sense of it, is widely separated therefrom, for the purpose of receiving 
forms which, in point of fact, have but little generic relationship to 
each other. Meanwhile, it is nevertheless a sort of refuge for various 
Diatoms which have not been thoroughly investigated, and which, 
in some cases, are known only so far as their side view is concerned. 
A portion of these, upon more mature knowledge, may be transferred to 
Dimeregramma, while others, from their Cocconeis-like habit, must cer- 
tainly be constituted as a special genus. Very numerous instances 
of forms belonging to the latter class have come under my notice; 
and I am convinced that they do not underlie the upper valves of 
Cocconeis—and for this reason, that I have never found associated with 
them valves of Cocconeis with a central nodule, or valves which in 
other details of structure would be supposed to correspond with them.” 
Verhand der K. K. Zool. Bot. Gesel., Band x11., 1862, p. 378. Two 
of the forms herein included—namely, Rhaphoneis amphiceros and 
Rhaphoneis rhombus, Smith has placed side by side, under the same 
generic name, with Doryphora Boeckiu, with which, beyond the fact 
of being stipitate, they have little in common. Rhaphoneis amphi- 
ceros was observed by Kiitzing 7m situ, and described and figured by 
him as stipitate. I am not aware whether, in the case of the other 
forms included, a similar fact has been noticed. Whatever presump- 
tion there may be in favour of the supposition, this feature cannot be 
as yet admitted as a general characteristic of the group. Odontidium 
Harrisoni, Wm. Sm., the frustules of which in general structure are 
similar to those of Denticula, as I have defined that genus, exhibits 
nevertheless a different habit of growth, the frustules being attached 
by a cushion or short stipes, and forming a filament, the several frus- 
tules adhering by their ends to one another. It seems then in this 
respect, as well as in the interrupted striation, to stand in close 
relationship with Rhaphoneis amphiceros, and on this account I include 
itin the same genus; not indeed because I feel quite satisfied on this 
point, but because, all things considered, I regard this most suitable 
as a provisional arrangement. 
