162 BRITISH 



We have not seen this species, nor has it been observed 

 since its original discovery by Wittrock. It seems to be well 

 characterized by its emarginate apices and its small central 

 protuberance. Its nearest ally is perhaps C. Phaseolus Breb. 



21. Cosmarium melanosporum Arch. 

 (PL LX, figs. 21-23.) 



Cosmarium melanosporum Arch, in Ann. Mag. Nat. Hist. 1883, 5th ser. 

 XII, p. 124 ; Cooke, Brit. Desm. 1887, p. 188 ; De Toni, Syll. Alg. 1889, 

 p. 1055 ; Roy & Biss. Scott. Desm. 1894, p. 167, t. 1, f . 14 ; West & G. 

 S. West, Alg. N. Ireland, 1902, p. 42. 



Ursinella melanospora Kuntze, E-evis. gen. plant. 1891, p. 167. 



Cells small, as long as broad, or sometimes a little 

 longer than broad, deeply constricted, sinus narrow, 

 widening outwards ; semicells transversely oblong, 

 basal angles well rounded, upper angles more rounded, 

 apex broadly convex. Side view of semicell circular. 

 Vertical view elliptic, ratio of axes about 1 : 1*7. 

 Cell- wall smooth. 



Zygospore globose and smooth, the wall of a very 

 dark brown colour, becoming black. 



Length 15-19 /x; breadth 15-19 /x; breadth of 

 isthmus 5-6*7 /x; thickness 7-9'6//,; diam. zygosp. 

 23-25-5 p,. 



ENGLAND. Leicestershire (Roif) . 



WALES.- -Bettws-y-coed, Capel Curig, Grlyder Fawr, 

 and Pen-y-gwryd, Carnarvonshire (Roy). 



SCOTLAND. Generally distributed (Roij Bissetf). 

 Outer Hebrides ! 



IRELAND.- -Dublin and Wicklow (Archer). Lough 

 Derryadd, Armagh ! 



Roy states that this species conjugates abundantly in 

 Scotland, and may be readily recognized by the smooth, 

 globular, very dark zygospore. We have only seen the 

 zygospores from the Outer Hebrides and from Ireland. 



C. melanosporum stands very near to G. tenue Arch., but 

 is distinguished by its more inflated semicells and by the 

 dark colour of the zygospore. The constriction is not so 

 deep in C. melanosporum as it is in C. tenue, and the vertical 

 view is more broadly elliptic. 



