DOCIDIUM. Ill 5 



iindulatum K'abcnh. Flor. Europ. Alg. Ill, 1868, p. 104. 

 Docidium <lilii!<il Km Lund. Dcsm. Suec. 1871, p. 88, t. 5, f. 12; Kirchn. 

 Ali;-. Srhl.-s. 1S7S, p. 144; Wolln, Dosm. U.S., 1884, p. 50, t. 50, f. :!i' : 

 !> Tnni, Syll. A1-. 1SS9, p. 87:*; West, Alg. W. Ireland, is'll', p. lis. 

 t. 19, f. 5 ; West & G. S. West, Some Desm. U.S. 1898, p. 285. 



Cells small, elongated, 14-20 times longer than 

 their diameter; semicells with 7-8 nodulose undula- 

 tions along each margin; apices dilated, truncate, witli 

 rounded angles ; basal plications 11-12, furnished 

 with granules as in D. Jlxml/nn (about 7 visible across 

 the base of the semicell) ; cell- wall smooth. 



Zygospore unknown. 



Length 178-246 //,; breadth (maximum) 1 2-16*5 ^ ; 

 breadth of apices 11*5-15 ^. 



SCOTLAND. Poolewe, Ross ; Glen Dole, Forfar ; 

 Rannoch, Perth (Roy 7??.s-.W/). Loch Morar, Inver- 

 ness ! Rhiconich, Sutherland ! Near Tarbert, Harris ; 

 near Balallan and near Callernish, Lewis, Outer 

 Hebrides ! 



IRELAND. Near Oughterard, Kylemore, and Oorid 

 Lough, Gal way ! Glengariff (Archer), Cromagloun, 

 Tore Mt., and Glen Caragh, Kerry ! 



(ti'nijr. Distribution. France. Norway. Sweden. 

 United States. Guiana. 



The Desmid we have placed under Docidium undulatum 

 Bail, is identical with that recorded by Lundell from Sweden 

 under the name of " Docidiwn dilatafum." It agrees much 

 more closely, however, witli Docidium mnlii.latum Bail, than 

 with the plant recorded by Cleve as Pleurotsenium dilatatum. 

 It possesses the undulated semicells exactly as figured by 

 Bailey, and also the ili/nfril, tnnn-ntr a />!</. \. Bailey re- 

 marked that both the base and npex of the semicells were 

 plicated, but all the British and American specimens we have 

 examined have only a plicated base. In fact, we know of no 

 Docidium with a plicated apex. Wolle's figure of Docidium 

 /n/ihi.laf-nm (Desm. U.S. 1884, pi. ii, fig. 5) does not represent 

 Bailey's species. 



D. undulatum is a very rare British species, and appears 

 to be principally confined to the western areas of Scotland 

 and Ireland. In these districts it is sometimes met with 

 abundantly; it is quite a characteristic species and seems to 

 be an Atlantic type. 



