188 BRITISH DESMIDIACE^]. 



A form of C. ve^ntum was observed from near Cocker- 

 mouth, Cumberland (PL XCII, fig. 5), in which the semicells 

 were less pyramidate, and the increase in size of the lateral 

 undulations from base to apex was not so strongly marked. 

 The central area was sparsely punctate. 



177. Cosmarium ftuasillus Lund. 

 (PL XCII, %. 3.) 



Cosmarium Quasillus Lund. Desm. Suec. 1871, p. 29, t. 3, f . 10; "VYolle, 

 see Desm. U. S. 1884, p. 84, t. 17, f. 13-15 ; De Toni, Syll. Alg. 1889, 

 p. 1020; Eoy & Biss. Scott, Desm. 1894, p. 173 ; Borge, Siissw. Chlorophy. 

 Archang. 1894, p. 29 ; Gutvr. Flor. Glon. Okolic Tarnapola, 1894, p. 98 ; 

 Nordst. Index Desm. 1896, p. 218 ; West & G. S. West, Alg. S. England, 

 1897, p. 490. 



C. irregulare Wolle in Bull. Torr. Bot. Club, 1877, p. 186 [vide WoUe, 

 Desm. U. S. 1884, p. 85". 



Ursinella Quasillus Kuntze, E-evis. gen. plant. 1891, p. 925. 



Cells of medium size, hexagonal in general outline, 

 a little longer than broad, very deeply constricted, 

 sinus narrowly linear with a dilated apex ; semicells 

 trapeziform or pyramidate-truncate, rather suddenly 

 narrowed from a broad flat base, basal angles obtuse 

 and minutely undulate-dentate, lateral margins undu- 

 late with the undulations increasing in size upwards, 

 apex a little produced, truncate and faintly biundulate, 

 apical angles obtuse, in the centre with a granulated 

 tumour, the granules being of large size and disposed 

 in subconcentric series ; cell-wall granulate, granules 

 arranged in radiating and subconcentric series, with a 

 small smooth space around the central tumour. Side 

 view of semicell ovate, with a verrucose tumour on 

 each side towards the base, apex rounded. Vertical 

 view rather narrowly elliptic, with a verruculose 

 tumour at the middle on each side, poles somewhat 

 pointed. Chloroplasts axile, with two pyrenoids. 



Zygospore unknown. 



Length 66-80 /x ; breadth 60-74 p.; breadth of 

 isthmus 17' 5-21 p.; thickness 44 p.. 



ENGLAND.- -E slier West-end Common and Wimbledon 

 Common, Surrey ! 



/ 



SCOTLAND.- -Xear Longside, Aberdeen ; Alva G-len, 

 Stirling (Roij $ Bistett). ' 



