202 BRITISH DESMIDIACE^E. 



inconceivable that the earlier investigators could have missed 

 such a striking and common Desmid, seeing that they re- 

 peatedly found most of its associates ; and, moreover, amongst 

 these associates they invariably recorded " C. margaritiferum.'' 



Hence, as we constantly find in bogs a Cosmarium as 

 common as C. margaritiferum was reported to be, of the same 

 size, and not differing materially from the published descrip- 

 tions of that species ; and as this Cosmarium occurs with the 

 same associates with which C. margaritiferum was generally 

 said to be found, and as it has exactly the same zygospore, we 

 are forced to the conclusion that IT is C. margaritiferum. 



At the same time this species is unquestionably identical 

 with Schmidle's " C. Malinrernianum var. Badense." Schmidle 

 was the first to point out the constantly flattened apex of the 

 semicells and the presence of the minute scrobiculations 

 between the central granules. We have recorded this plant 

 under the erroneous name of " C. confusum var. regularius ' 

 from many parts of the British Islands, and the Desmid 

 described as " C. coufusum subsp. amliguum" from the west 

 of Ireland is C. margaritiferum. in its most typical form. 



C. margaritiferum is widely distributed in the Spliagnum- 

 bogs of the British Islands, especially in the western boggy 

 areas. It is more rarely found at the boo-o-y margins of 



/ <_> ~ / o 



lakes and amongst the leaves of LittoreHa lacuxtri* and Isoetes 

 lacustris. 



Special reference is also necessary to other so-called species 

 which should merely be regarded as forms of C. margariti- 

 ferum. The first of these is Cookers "Cosmarium confusum," 

 which was a name 2'iven bv Cooke in 1887 to " C. Brebissonii 



*/ 



a genuina Jacobs/' The Desmid figured by Jacobsen only 

 differs from C. margaritiferum in the spine-like adornment of 

 the basal angles of the semicells, a character which we are 

 inclined to think has been portrayed in an exaggerated 

 manner. This basal i spine ' is most probably an elongated 

 conical granule, and an approximation to this condition is 

 often observed in specimens of C. margaritiferum (vide PI. 

 LXXXIII, fig. 4), in which the basal granule is larger than 

 any of the others and of a decidedly conical shape. 



Another form is that which was temporarily referred by 

 Nordstedt to C. confusum as " var. regularius." This appears 

 to differ from C. margaritiferum only in having a granulated 

 apex, and perhaps in its somewhat smaller dimensions. 



A third form is the Desmid which has come to be known 

 as " Cosmarium Kirclineri Borg." This was first described as 

 a variety of C. trachypleurum Lund., but it differs from typical 



