O’Mrara—Report on the Irish Diatomacee. 321 
this genus has not hitherto been described with sufficient accuracy 
for their satisfactory diagnosis, and consequently its relations with 
other genera have been very variously represented. Kiitzing in- 
cludes it among the Naviculee; Smith places it between Amphi- 
prora and Navicula, while Ralfs, Grunow, and Heiberg, agree in 
assigning to it a position of near relationship to the Nitzschice. 
The remarks of the last named author are noteworthy :—‘‘ Amphi- 
pleura is a genus which stands in need of a more precise reyl- 
sion. Grunow, in his first treatise, placed the genus in the group 
Surirellese, with which it has no very close relationship; but sub- 
sequently this author established the genus as the type of a special 
group, Amphipleuree, and at the same time gaye a valuable contribu- 
tion towards a more precise limitation of the genus: but notwithstand- 
ing, much remains still to be done. JI have placed the genus with the 
Nitzschiee, because Amphipleura sigmoidea, the only species tho- 
roughly examined by me, seems to agree essentially with Nitzschia, 
and in fact to possess the same unsymmetrical relation of the connect- 
ing membrane with the front view. As to the other of the under- 
named species (Amphipleura pellucida), [have not as yet had sufficient 
material to institute a more exact examination, and have been able 
only to satisfy myself as to its identity with the species of the author 
named.””—De Danske Diat., p. 116. The above remarks indicate the 
source of the confusion which exists, namely, the supposition that the 
form described as Amphipleura sigmoidea belongs to the genus 
Amphipleura; I regard it as not at all distinguishable from Nitzschia 
sigma. Assigning this latter form to its proper place, we have a 
distinct and satisfactory diagnosis of the genus Amphipleura, founded 
on the presence of the median line without a central nodule, and the 
elongated character of the end nodules, as well as the presence of the 
submarginal lines. Referring to the last named peculiarity of struc- 
ture, Smith notices Ehrenberg’s ideal transverse section of the frus- 
tule, ‘‘ which represents the ridges as springing from the surface of a 
convex valve, having between them a depression which corresponds 
with the ordinary median line of the Navicule,”’ and adds, ‘‘ I am 
unable to confirm this description.””—B.D., Vol.i., p. 45. Grunow, 
however, asserts that ‘‘ each valve has three kcels; the two submargi- 
nal ones springing out so far in one aspect as to stand on the valves at 
right angles with the margin. In the aspect of the entire frustule 
as seen from the side, the submarginal keels appear, and the median 
line forms the contour of the valves.’”’—Verhand. der K. K. Zool. Bot. 
Gesel. Band xii., 1862, p. 467. 
Amphipleura pellucida, (Kiitz.) Fresh water. 
Valves narrow, lanceolate; strie obscure. (Pl. 29, fig. 8.) 
Kutz. Bae. p, 103, Tein, fig. 52; To xxx., fig. 84, ‘In ‘neither of 
these figures is the peculiar form of the end nodules noticed. Wm. 
sm., B.D., Vol. 1, p. 45, Pl. xy., fig. 127. Here the valve is repre- 
