O'Meara — Report on the Irish Diatomacece. 321 



this genus has not hitherto been described "svith sufficient accuracy 

 for their satisfactory diagnosis, and consequently its relations with 

 other genera have been very variously represented. Kiitzing in- 

 cludes it among the Naviculese ; Smith places it between Amphi- 

 prora and Xavicula, while Ealfs, Grunow, and Heiberg, agree in 

 assigning to it a position of near relationship to the IS^itzschieae. 

 The remarks of the last named author are noteworthy: — "Amphi- 

 pleura is a genus which stands in need of a more precise revi- 

 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, Amphipleurese, and at the same time gave a valuable contribu- 

 tion towards a more precise limitation of the genus : but notwithstand- 

 ing, much remains still to be done. I have placed the genus with the 

 ^J^itzschiese, because Amphipleura sigmoidea, the only species tho- 

 roughly examined by me, seems to agree essentially with Xitzschia, 

 and in fact to possess the same unsymmetrical relation of the connect- 

 ing membrane with the fi'ont view. As to the other of the under- 

 named species (Amphipleura pcllucida), I 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 Amphipleui'a sigmoidea belongs to the genus 

 Amphipleura ; I regard it as not at all distinguishable fi'om IS'itzschia 

 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. Eefening 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 ordinaiy median line of the yaviculas," and adds, "I am 

 unable to confirm this description." — B.D., Tol. i., p. 45. Grunow, 

 however, asserts that " each valve has three keels ; 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 entii'e fmstule 

 as seen from the side, the submarginal keels appear, and the median 

 line forms the contour of the valves." — Yerhand. der K. K. Zool. Eot. 

 Gesel. Band xii., 1862, p. 467. 



Amphijjleura pellucida, (Kiitz.) Freshwater. 



Valves narrow, lanceolate; striae obscure. (PI. 29, fig. 8.) 



Kiitz. Bac, p. 103, T. iii., fig. 52, T. xxx., fig. 84. In neither of 



these figures is the peculiar form of the end nodules noticed. Wm. 



Sm., B.D., Vol. i., p. 45, PI. xv., fig. 127. Here the valve is repre- 



