O’Mreara—Report on the Irish Diatomacee. 329 
horst, but Heiberg rejects it as being unnecessary, the forms being, as 
he thinks, ranged properly with the Navicule. 
Dickieia ulvoides, (Berk.), Marine. 
Gelatinous frond, more or less perfectly ovate; entire, and having 
a distinct pedicel; valves linear, elliptical ; central nodule transversely 
dilated ; strie fine, parallel. (Pl. 29, fig. 14.) 
Berkeley and Ralfs, Ann. Nat. Hist., Series 1., Vol. xiv., Pl. ix., 
Kiitz. Bac, p.119. Wm.S8m., B.D., Vol. i1., p. 66, Pl. liv., fig. 342. 
Ralfs, in Pritch., p. 925, Pl. xv., fig. 31. Rab. Fl. Eur., sect. 1, 
p. 264. 
Greystones, Co. Wicklow. 
Dickieta pinnata, (Ralfs), Marine. 
Frond lasciniated ; valves narrow, elliptical; strie fine, parallel; 
nodule small, round. 
Ralfs. Ann. Nat. Hist., 2nd Series, Vol. viii., Pl. v., fig.6. Ralfs, 
am Peter p.:92o,- ‘Wm. Sur; BoDT Vol: i;'px 66; Pl. liv. fig:'34s. 
Rab. Fl. Eur., sect. 1, p: 264. 
On piles of the wooden bridge, Dollymount strand; Wooden piles 
on strand, Clontarf ; Sea-weeds, Malahide ; Ireland’s eye; Rock-pools, 
Ballybrack, Co. Dublin: in the last named locality it occurs in greatest 
abundance. Larne, Co. Antrim. 
Genus III. Correronema, De Bréb. 
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 Brébisson 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. Rabenhorst, 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. Ralfs 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 
