COSMAEIUM. 145 



granules minute, within the crenate marsrin furnished 



o m O 



with minute granules, often disposed in pairs or in 

 threes, more or less concentrically and radiately 

 arranged, with 12-15 short vertical ridges across the 

 base of the semicell, each ridge 2-4-granulate, area 

 immediately above this basal zone smooth. Side view 

 of semicell sub-ovate, slightly tumid at the base on 

 each side, upper half broadly rounded and 10-12- 

 undulate. Vertical view broadly elliptic, with some- 

 what pointed poles, ratio of axes 1 : 1'4, each side 

 with 12-15 granules. Chloroplasts axile, one in each 

 semicell, with a central pyrenoid. 



Zygospore unknown. 



Length 35-42 p.; breadth 23-29 p. ; breadth of 

 isthmus 14-20 \L ; thickness 23-26 p.. 



ENGLAND. Xear Cowside Beck, Arncliffe, and in 

 Heseltine Ghvll on Penyghent. AV. Yorks ! 



i> / O 



Geogr. Distribution.- -Norway. Austria. Poland. 



This characteristic species was originally described by 

 Nordstedt from Xorway, where it was found among mosses 



on wet mountain rocks. We have onlv found it on vertical 



<j 



dripping faces of limestone rocks in the Pennine Chain, and 

 several times in pure masses. 



146. Cosmarium isthmium West. 

 (PL LXXYII, figs. 7-10; PI. XCIV, fig. 2.) 



Cosmarium excavatum Nordst. forma duplo-major Wolle, Desm. U. S. 1884, 



p. 77, t. 53, f. 14, 15 [not Lundell, 1871~. 

 C. isthmi".,,' West, Alg. N.Wales, 1890," p. 290, t. 5, f. 19; Alg. Engl. 



Lake Distr. 1892, p. 729 ; Nordst. Index Desm. 1896, p. 149 ; West & 



a. S. West, Alg. S. England, 1897, p. 491. 



Cells rather small, rather more than 1-J times as 

 long as broad, fairly deeply constricted, sinus widely 

 open, forming a semicircular or semi-elliptic excava- 

 tion : semicells semicircular. basal ano-les subrectano-ular 



' ' O O 



and not rounded, cell-wall ornamented with rounded 

 granules arranged in 8-10 vertical series, about 7 

 granules in each series, slightly reduced at the apex 

 and 16-20 Q-ranules showing at the maro-in. Vertical 



o o o 



view almost circular (very slightly compressed), with 



VOL. III. 10 



