272 Proceedings of the Royal Irish Academy. 



being only a mucous cushion or stipes, and on these grounds the genus 

 Isthmia ought to be excluded. In the case of Hydrosera ("Wallich), 

 the fi'ustules are not symmetrical, processes occuiTing on the one ralre, 

 and not on the opposite one. 'W'allich's description is "on one side 

 only, with a remarkable series of aperture-like appendages." "Wallich 

 on Triceratium, Q. J. IT. S., July, 1858, p. 251. Por which, reason I 

 consider the genus Hydi'osera is not properly comprehended in the 

 group. The species marked by an angular outline of the valves as 

 Triceratium, Amphitetras, &c., however closely related to the Biddul- 

 phieae, seem however to possess such distinctive peculiarities of struc- 

 tui'e as to justify theii" being placed in a separate group ; and if any 

 fonns of the genus Hemiaulus had occuiTed in Irish localities, I would 

 have been disposed to include them with the Biddulphiese as Eaben- 

 horst has done in his Flora Europea Algarum. 



Various' generic nauies have fi'om time to time been introduced by 

 diiferent writers to designate the forms of this group, in consequence 

 of which much confusion has arisen, to obviate which a few remarks 

 are here necessary. 



The generic name Biddulphia was first adopted by Gray, and 

 along with Biddulphia pulchella embraced some heterogeneous forms, 

 which latter were afterwards removed to their proper places. Agardli 

 then established the genus Odontella to receive the single species now 

 known as Biddulphia aurita ; Ehr'enberg ha'^T.ng applied the name 

 Odontella to a species of Desmid, as Boper informs us, Q. J. IM. S., 

 Oct., 1858, p. 3, substituted for it the designation Denticella, which 

 was thus equivalent to Agardb's Odontella. The forms included in 

 these genera, Biddulphia and Denticella, were filamentous ; and 

 Ehrenberg having found kindred fonns which, without sufficient 

 esamination, he considered to be simple, adopted the genera Zygoceros 

 and Cerataulus, the foiTaer for those free fonns, as he thought them 

 allied to Biddulphia, the latter to Denticella. Some of these genera 

 have been retained by succeeding writers, but Smith in his Synopsis 

 has, as I think, wisely dispensed with these superfluous subdivisions, 

 and included the forms contained in them under the one generic 

 name. 



Babenhorst, in his Elora Eui'opea Algarum, places the Biddulphiefe 

 in close connexion with the septate fonns, supposing, as I imagine, that 

 the costas on the valves of Bid. pulchella and other species with un- 

 dulate sui^Eaces are septa. On this subject the observations of Smith 

 are worthy of notice : " The existence of septa inB. pulchella is by 

 no means to be admitted, though the costse may occasionally project 

 into the interior of the cells." B. D., Tol. ii., p. 49. 



Genus I. BiDDrxrniA, Gray. 



Processes projecting outwards at a more or less acute angle fi-om 

 the plane of the base. 



