O'Meara — Report on the Irish Diatomacece. 329 



"horst, but Heiberg rejects it as being unnecessary, the forms being, as 

 he thinks, ranged properly with the Naviculse. 



BicMeia ulvoides, (Berk.), Marine. 



Gelatinous frond, more or less perfectly ovate ; entire, and having 

 a distinct pedicel; valves linear, elliptical ; central nodule transversely 

 dilated; stride fine, parallel. (PI. 29, fig. 14.) 



Berkeley and Ralfs, Ann. Nat. Hist., Series 1., Yol. xiv., PI. ix., 

 Kiitz. Bac, p. 119. Wm. Sm., B. D., Vol. ii., p. 66, PI. liv., fig. 342. 

 Ealfs, in Pritch., p. 925, PI. xv., fig. 31. Rab. Fl. Eur., sect. 1, 

 p. 264. 



Greystones, Co. "Wicklow. 



BicJcieia pinnata, (E,alfs), Marine. 



Prond lasciniated ; valves narrow, elliptical ; striae fine, parallel ; 

 nodule small, round. 



Ealfs. Ann. Nat. Hist., 2nd Series, Vol. viii., PI. v., fig. 6. Ralfs, 

 in Pritch., p. 925. Wm. Sm., B. D. Vol. ii., p. 66, PI. liv., fig. 343. 

 Eab. PL Eur., sect. 1, p. 264. 



On piles of the wooden bridge, Dollymount strand ; Wooden piles 

 on strand, Clontarf ; Sea- weeds, Malahide ; Ireland's eye ; Eock-pools, 

 Ballybrack, Co. Dublin : in the last named locality it occurs in greatest 

 abundance. Larne, Co. Antrim. 



Genus III. Colletoxeiia, De Breb. 



Gelatinous frond filiform, simple or sparingly divided at the ends. 



The first known forms of this genus were discovered by Thwaites, 

 •and published by him in Ann. Hist., March, 1848, under the generic 

 name of Schizonema. De Brebisson subsequently separated these 

 forms from Schizonema, and instituted the present genus for their 

 reception ; the distinguishing characters being their fresh water habi- 

 tat, and the simple tubular frond. Whatever value may attach to 

 the latter peculiarity, the former is utterly untenable as a generic dis- 

 tinction. Smith alleges that in this genus the frustules are more 

 firmly silicious than in Schizonema, a statement I cannot corroborate ; 

 but even though it admitted of no doubt, this fact could scarcely be 

 regarded as a sufficient generic distinction. Eabenhorst, Siissw. Diat., 

 p. 51, who himself observed none of the species, adopts the genus, 

 characterising it by the fact of the frustules occurring in rows within 

 a structureless gelatinous investment. Ealfs adopts Smith's definition, 

 but doubts "if any of the above characters sufficiently distinguish 

 Colletonema from the allied genera," in Pritch., p. 926. Grunow's 

 observations on the genus are noteworthy; he says: "The genus 



