106 BRITISH DESMIDIACE^E. 



A somewhat smaller variety with the basal angles 

 of the semicells rounded to such a degree that the 

 semicells are almost obversely semicircular. 



Length without spines 23-26 /A, with spines 5 1-54 ju ; 

 breadth without spines 25-28 /x, with spines 45-54 /x; 

 breadth of isthmus 6*58 /x. 



WALES.- -Capel Curig and Llyn-y-cwm-ffynon, Car- 

 narvonshire ! 



SCOTLAND.- -Ehiconich, Sutherland ; Lewis and 

 Harris, Outer Hebrides ! 



IRELAND.- -Near Grlenties and Lough Anna, Donegal ! 



Ballvnahinch and near Roundstone, Galwav ! Grlen- 



j / 



garriff, Cork ! 



AVe had for some time erroneously regarded this Desmid 

 as a form of Arthrodesmus Incus, as its proper place in a 

 systematic scheme appears to he with A. Bulnheimii. No 

 form of A. Incus ev r er possesses a closed sinus with a dilated 



extremitv. and we consider that this one character is alooe 

 * 



sufficient to relegate it to A. Bidnheimii. 



A. Bulnheimii var. sulnncus is a western type of Desmid, 

 and in parts of Lewis, Harris, and the west of Ireland it is 

 sometimes very abundant. 



8. Arthrodesmus convergens Ehrenb. 

 (PI. CXVI, figs. 4-13.) 



Arthrodesmus convergent Ehrenb. Infus. 1838, p. 152, t. 10, f. 18 ; Hass. 

 Brit. Freshw. Alg. 1845, p. 357, t, 85, f. 9 ; Ralfs, Brit, Desm. 1848, 

 p. 118, t. 20, f. 3; Kiitz. Spec. Alg. 1849, p. 170; Arch, in Pritch. 

 Infus. 1861, p. 737; Lund. Desm. Suec, 1871, p. 54; Kirchn. Alg. 

 Schles. 1878, p. 156; Wolle, Desm. U. S. 1884, p. 95, t. 23, f. 19-21; 

 Cooke, Brit. Desm. 1887, p. 136, t. 47, f. 1 ; Hansg. Prodr. Algenfl. 

 Bbhm. 1888, p. 203, f. 117, and p. 251; Nordst. Freshw. Alg. N. Zeal. 

 ivss, p. 45 ; De Toni, Syll. Alg. 1889, p. 1058; West, Alg. N. Wales, 

 1890, p. 292 ; Heimerl, Desm. alp. 1891, p. 603 ; West, Alg. W. Ireland, 

 1892, p. 169 ; Alg. Engl. Lake Distr. 1892, p. 730 ; Lutkem. Desm. 

 Attersees, 1893, p. 559 ; Koy & Biss. Scott. Desm. 1894, p. 40 ; W. & G-. 

 S. West, Some N. Amer. Desm. 1896, p. 254, t, 16, fig. 3 ; Nordst, Index 

 Desmid. 1896, p. 81 ; W. & G. S. West, Alg. S. England, 1897, p. 497 ; G. S. 

 West, Variation Desm. 1899, p. 397, 398 and fig. xylogr. 4 ; Lutkem. 

 Desm. Millstilttersees, 1900, p. 70 ; W. & G. S. West, Alga-fl. Yorks. 

 1901, p. 108 ; Alg. N. Ireland, 1902, p. 58 ; Him, Desm. Finland, 1903. 

 p. 5 ; W. & G. "S. West, Scott. Freshw. Plankton, I. 1903, p. 528 ; 

 Borge, Alg. erst. Eegnell. Exped., II. Desmid. 1903, p. 103 ; Larsen, 

 Freshw. Alg. E. Greenland, 1904, p. 81 ; W. & G. S. West, Freshw. Alg. 

 Orkneys and Shetlands, 1905, p. 23 ; C ashman in Ehodora, vii, 1905, 



