O'Meara — Report on the Irish Diatomacece. 337 



being that while in the former case the valve is rounded at the ends, in 

 the present case they are acute. I have sometimes found both species 

 in the one gathering. 



Agardh. Syst., p. 10. Id. Consp., p. 20. Grev. Brit. TL, p. 412. 

 Harvey's Manual, p. 212. Kiitz., Bac, p. 118, T. xxvi., fig. 3. Wm. 

 Sm., B. D., Vol. ii., p. 77, PI. Iviii., fig. 366. Ealfs, in Pritch., p. 928. 

 Rab., PL Eur., sect. 1, p. 272. 



Eathlin Island, Carrickfergus, Carnlough Bay, Co. Antrim — all 

 collected by Dr. David Moore. Eiver I^annywater, Laytown, Co. Meath. 

 Merrion, Co. Dublin. 



(b). AcMamydicB. FrustuJes icithout a gelatinous investment. 



Genus YI. Diades^xis, Xiitz. , 



Erustules united in a filament. 



Diadesmis ivilliamsonii, (^"m. Sm.) Marine. 



On front view margins of frustules undulate, and exhibiting the 

 striation of the valve ; on side view, valve linear, acuminate at the 

 ends. Striae moniliform. (PI. 29, fig. 21.) 



This form was first partially described by Wm. Smith, B. D., Yol. 

 ii., p. 14, PI. xxxiii., fig. 287, who, having seen only the front view 

 so accurately figured by him, doubtfully referred it to the genus 

 Himantidium. Subsequently Gregory, who had opportunity of more 

 thoroughly investigating it, transferred it to the genus Diadesmis, to 

 which it properly belongs. Grunow refers this species to the genus 

 Dimeregramma, and makes the following observations : — " Of the 

 Eunotia-like structure of the same there is no cjuestion ; the margins 

 of the front view are never so distinctly triundulate as in Smith's 

 description ; for the most part the middlemost elevation is found much 

 stronger than the other two, in consequence of which it approaches 

 Dimeregramma minor." — Yerhancl. der K. K., Zool. Bot. Gesel., Band 

 xii., 1862, p. 377. 



Gregory, Diat. of Clyde, p. 25, PI. x., fig. 40, in which both side 

 and front views are accurately delineated. EaKs, in Pritch, p. 923. 

 Eab. PL Eur., sect. 1, p. 260. 



Erom stomachs of Ascidians, Eoundstone Bay, Co. Gal way. 



Genus YII. Beebissonia, Grunow. 

 Frustules simple, stipitate. 



The only species of this genus was by Smith described and figured 

 under the name of Doryphora Bocckii. The genus Doryphora had 



