42 BRITISH DESMIDIACE^:. 



Lewis, and Loch a Mhorghain, Harris, Outer Hebrides ! 

 Orkneys and Shetlands ! 



IRELAND.- -Donegal ! Clare Island, Co. Mayo! Gal- 

 way ! Kerry ! Armagh ! Plankton of (lalway ! 



Geogr. Distribution. Germany. Finland. India. 

 Australia. United States. 



This variety seems to differ from typical St. Avicula in the 

 form of its semicells as well as in its stronger granulation. In 

 the front view the semicells are more cuneate, with sides and 

 apex nearly straight, and the angles of the cell are very slightly, 

 almost imperceptibly, produced. In the vertical view the sides 

 are more concave than in the type. 



69. Staurastrum subcruciatum Cooke & Wills. 

 (PL CXXXIII, figs. 6, 7.) 



Staurastnitii subcruciatum Cooke & Wills in Cooke, Brit. Desm. 1887, p. 148, 

 t. 51, f. 3 ; De Toni, Syll. Alg. 1889, p. 1158 ; Schmidle, Alg. Geb. Ober- 

 rheins, 1893, p. 553 ; West & G. S. West, Alga-fl. Yorks. 1902, p. 97. 



Cells a little broader than long, deeply constricted, sinus 

 acute and almost rectangular, opening widely ; semicells 

 somewhat triangular or lunate, dorsal margin concave, 

 slightly convex in the middle, ventral margin approxi- 

 mately semicircular, angles slightly produced obliquely 

 upwards and tipped by two diverging spines which lie 

 in the same vertical plane ; cell wall covered with tiny 

 granules, which are arranged in concentric series round 

 the angles and are reduced or wanting more remote 

 from them. Vertical view triangular, lateral margins 

 concave and angles slightly produced; centre of apex 

 nearly smooth. 



i/ 



Zygospore unknown. 



Length 30-31 pi ; breadth 33-35 ^ ; breadth of isth- 

 mus 7 '5 [i. 



ENGLAND.- -Wigton Moor, W. Yorks! Dartmoor, 

 Devon (PI arris). 



WALES. Capel Curig, Carnarvonshire ! (Cooke & 

 Wills). 



SCOTLAND.- -Near Aberdeen ! 



