O'Meara — Report on the Irish Diatomacece. 253 



to what he had noticed in Meridion circulare and M. constrictum, 

 Himantidium Soleirolii, Odontidium anomalum, and Achnanthes sub- 

 sessilis. I add the interesting description given by Piitzer of an ano- 

 malous procedure noticed by Fr. Schmitz in the development of 

 Orthosira spinosa, as likely to throw some light on the subject. *' A 

 separation of the firstling-cell followed, not immediately, but a devia- 

 tion occurred analogous to what has been described in the case of 

 JS'avicula ambigua. First one girdleband was developed, the length 

 of which was about that of the radius of the cell. This girdleband, 

 according to Fr. Schmitz, was attached only to one valve; that which 

 ought to have been connected with the other valve, if it existed at 

 all, was only rudimentary. Then the plasm moved about only in that 

 haK of the cell to which the girdleband adhered, and secreted a new 

 valve, which, as might be expected, was parallel to the original one 

 ■destitute of the girdleband. In the cell so originating, division then 

 took place in the normal manner, only that the one end-cell of the fila- 

 ment in course of formation, instead of two valves possessed three. 

 Inasmuch as a small portion of the plasm remained behind, between 

 the two parallel valves, and then died off, Fr. Schmitz was inclined 

 to think the procedure was an abortive attempt at self-division, one 

 portion of the plasm being too small to develop itself into a daughter- 

 cell." Ileber Bau und Entwicklung der Bac, p. 135. 



Ditch on bank of Royal Canal, near Kilcock, Co. Kildare. It is 

 likely this species is more common than it appears from the few lo- 

 calities assigned to it, as in its normal condition it may be easily con- 

 founded with Melosira varians. 



Orthosira oriehalcea, (Wm. Sm.) Freshwater. 



The circle of puncta that in most of the species of this genus runs 

 parallel with the suture is not observable in this. Spines on junction 

 surfaces distinct ; valve not striated on the side view, except on the 

 margin, where the points of the spines appear as small puncta. Frus- 

 tules striated' on front view. Striae fine, punctate, parallel. (PI. 26, 

 fig. 8.) 



Ralfs and Eabenhorst have referred this species to IVIertens on the 

 authority of Kiitzing, who has figured and described a form under this 

 specific designation. The figure of !Melosira oriehalcea, Bac, T. ii., 

 fig. 14, is by no means definite, and one feature in the description 

 suggests the impression that he had quite a different species in view. 

 '' Sub epidermide silicea leviter bis contractis," Bac. p. 54, may pos- 

 sibly refer to Orthosira spinosa, but not to Orthosira oriehalcea, as 

 figured by Smith, to whom Heiberg considers the species should be 

 attributed, as he was the first to give a description and figure by 

 which it could be satisfactorily identified. Heiberg makes the follow- 

 ing skrewd observation under Orthosira oriehalcea : — " The figure by 

 which Smith describes the process of conjugation in the species under 

 consideration, and which he copied from Thwaites' original delineation, 



2L2 



