50 BRITISH DESMIDIACE^E. 



obliquely-truncate or acutely-rounded basal angles, 

 and with an undulation between the basal ansfle and 



o 



the upper apiculatioii ; central protuberance triverru- 

 cose or granulate; semicells sometimes with a few 

 granules within the marginal undulations. 



Length 36'5-53ju; breadth 22'5-34^; breadth of 

 isthmus 3*8-9 p; thickness 15-24 /x. 



SCOTLAND. Near Tarbert, Harris, Outer Hebrides I 



IRELAND. Slieve Donard, Down ! 



Geogr. Distribution. Nova Zembla. 



Var. ornatum West. (PI. XXXVIII, fig. 26.) 



E. elegans var. ornatum West, Alg. Engl. Lake Distr. 1892, p. 723, t. 9, f . 9 ; 

 West & G. S. West, Some N. Amer. Desm. 1896, p. 244. 



Cells slightly larger than in the type ; basal angles 

 furnished with a granule and also with one just within 

 the margin, with an undulation between the base and 

 the upper apiculation on each lateral margin ; with six 

 large rounded granules in the centre of the semicells 

 near the base (in 2 series of 3) and with one on each 

 side of the apical incision. 



Length 45-47 /i ; breadth 28-29 p ; breadth of 

 isthmus 8-10 /i ; thickness 14-1 7*5 /x. 



ENGLAND. Harrop Tarn, Cumberland ! Stickle Tarn 

 and Bowness, Westmoreland ! 



WALES. Grlyder Fach, Carnarvonshire ! 



t/ 



SCOTLAND. Glen Shee, Perthshire ! 

 Geogr. Distribution. United States. 



This is a very characteristic variety differing materially 

 from other forms of E. elegans in the six central granules. 



Var. ornithocephalum (Benn.) nob. (PL XXXVIII, 



fig. 27.) 



E. ornithocephalum Benn. Freshw. Alg. Eng. Lake Distr. 1886, p. 9, t. 1, 

 f . 12 ; Cooke, Brit. Desm. 1886, p. 78, t, 35 (after Bennett) ; De Toni, 

 Syll. Alg. 1889, p. 1107 ; Benn. Freshw. Alg. Hamps. and Devon,. 

 1890, p. 7. 



Helierella ornifhocepliala Kuntze, Revis. gen. plant. 1891, p. 899. 



Cells somewhat larger than in the type : almost 

 twice as long as broad, basal angles rounded and 



