><> I5EITTSH DESMiniAC'K.E. 



apex, and may make about l turns in the whole length 

 of the cell; but in the majority of specimens they are 

 much straighter than this, and in some are longitudinal 

 although not quite straight. They are not always continuous 

 from end to end, but often run only part of the distance and 

 tin 'n fade away or join with a neighbouring striolation. In 

 many cases they are very irregular, and a reticulation is 'often 

 present joining together several, or all of them. In some 

 individuals this reticulation is concentrated in the middle of 

 the cell ; in others there is a marked reticulation at the end 

 of the cell, and sometimes a reticulated zone is present just 

 below the apex. Most specimens have a distinct convex 

 apical cap which is strongly punctate, the punctulations being 

 continuous with those between the striolations. All examples 

 possess punctulations between the striolations, however minute 

 they may be. There is every indication that the striolations 

 are internal thickenings of the cell-wall. In the majority of 

 instances the edges of the striolations are not smooth, but 

 exhibit various degrees of roughness, and in some specimens 

 under a particular focus a reticulation is perceived to exist 

 between the punctulations, apparently connecting the striola- 

 tions together. 



The vai-iations in the outward form of this species are due 

 to the irregularity in the position of the sutures. 



There is no doubt whatever that Rail's confused this plant 

 with Peninm vtnnjaritaceuni, and he unquestionably described 

 and figured both vegetative specimens and zygospores under 

 the name of "P. margaritaceum j punctatum." It was one of 

 tin- first Desmids we observed when examining some material 

 of our own collecting from one of the favourite localities of 

 Ralfs -near Penzance. 



17. Penium polymorphum Perty. 

 (PI. IX, figs. 9-11.) 



Closterium polymorphum Perty, 1849. 



Penivm polymorjihum Perty, Kleinst. Lebensf. 1852, p. 207, t. 16. f. 15; 



Kabenh. Flor. Europ. Algar. Ill, 18G8, p. 123 (in part) ; Lund. Desin. 



Suec. 1871, p. 86, t. 5, f. 10 ; Wolle, Desm. II. S. 1884, p. 36, t. 5, f. 12 ; 



Norclst. Freshw. Alg-. N. Zeal. 1888, p. 71 ; West, Alg. W. Ireland, 1892, 



p. 128 ; Alo-. Engl. Lake Distr. 1892, p. 721 ; Eoy & Biss, Scott, Desm. 



1894, p. 253 ; Nordst. Index Desm. 1896, p. 203 ; West & G. S. West, 



Alg. S. England, 1897, p. 479; Alga-fl. Yorks. 1900, p. 46; Alg. X. 



Ireland, 1902, p. 22. 



Cosmai-i a in polymorphum Jacobs. Desm. Danem. 1876, p. 201. 

 /Vin'ioii polymorphum forma alpicola Heimerl, Desm. alp. 1891, p. 590, 



t. 5, f. 4. 



polymorphum var. LwteZeZZu Schmidle, Alg. Bern. Alp. 1894, p. 89. 



