Desmidiacecv 



155 



8-6 /i). M. caldariorum (Lagerh.) Hansg. is an attenuated species which 

 occurs in greenhouses, forming a thin mucilaginous stratum on damp walls, 

 etc. (length 2746 p ; breadth 1O5 11'5^). M. Endlicherianum Nag. is the 

 most frequent of the free-floating forms (length 25 27 p ; breadth 8'5 9-5 /*), 

 and J/. purpureum W. & G. S. West and M. molascens De Bary contain 

 phycoporphyrin. The zygospores of species of this genus are generally poly- 

 hedral with thick brown walls. 



Fig. 54. A, Spirottenia condensata Breb., from Rhiconich, Sutherland ( x 334), 

 showing parietal chloroplast. B, Sp. obscura Balfs, from Terrington, N. Yorks. 

 ( x 435), showing the axile, cristate chloroplast. C, zygospore of Sp. truncata 

 Arch. ( x 250, after Archer). D, Mesotcenium De Greyi Turner, from near 

 Settle, W. Yorks. ( x 435). E and F, M. macrococcum (Kiitz.) Roy & Biss., 

 from near Giggleswick, W. Yorks. ( x 334). G, zygospore of M. chlamydosporiim 

 De Bary, from Mayo, Ireland ( x 334). H and I, Cylindrocystis Brebissonii 

 Menegh., from Helvellyn, Westmoreland; H, vegetative cell; I, zygospore 

 ( x 435). J, Cyl. diplospora Lund., from Galway, Ireland ( x 435). K, Netrium 

 Digitus (Ehrenb.) Itzigsh. & Rothe, from Moel Siabod, N. Wales ( x 435). 



Genus Cylindrocystis Menegh., 1838. The cells are straight 

 and cylindrical, averaging twice longer than the diameter, and 

 they may or may not possess a slight median constriction. The 



