PROCEEDINGS OF SOCIETIES. 293 



and Peniuin agreed, the relative position and arrangement of the 

 parent conjugated cells afforded characters of a certain amount of 

 value. 



There was also shown the zygospore of a minute species of 

 Cosmarium, close to C bioculatum on the one hand, and to C. tinc- 

 tum on the other ; this is globular and smooth, and quite destitute 

 of spines, and apparently very large in proportion to the dimen- 

 sions of the parent forms. The segments of this species are elliptic 

 and smooth, constriction deep, end view elliptic. But irrespective 

 of dimensions and general contour giving quite a different impres- 

 sion to the eye, this form is distinguished from C. hioculatum, 

 inasmuch as the zygospore of that species has spines. "Whilst, 

 indeed, that of C. tinctum is without spines, the present plant in 

 itself is a good deal larger, and wants the reddish colour so charac- 

 teristic in that species. In its smooth zygospore it agrees with 

 C. pygmcBum (Arch.), but it is quite distinguished therefrom by 

 the elliptic, not sub-quadrilateral, segments. He would name this 

 marked little species now exhibited Cosmarium tenue. 



Another new zygospore, shown by Mr. Archer, was that of a 

 Cosmarium rather common with us, but rarely found conjugated ; 

 but he had taken it at least three times this spring, and from as 

 many distinct sources. This is a form he had not as yet been able 

 to determine, but was desirous to see one or two examples • of 

 certain allied Continental forms for that purpose. It is somewhat 

 like Cosmarium margaritiferum, but with us more frequently 

 presents itself. Although both may be called common, they do 

 not seem to occur, like some others, in quantities and unmixed 

 with other forms. In fact, it would almost appear as if Ealfs 

 himself may have confused tliis and C. margaritiferum together, 

 judging from his figures. Thus, it may be conjectured that Half's' 

 figure (' British Desmidiese,' pi. xvi, fig. 2 (T) may represent the 

 present form (the zygospore partially formed only), and that fig. 2 

 a and h may be the true G. margaritiferum, the zygospore of which 

 is shown at pi. xxxiii, fig. 6 h. The present plant can be 

 detected with the greatest readiness, and distinguished from 

 C. margaritiferum, xxndev the very lowest power that reveals either, 

 by the semicircular shape of the segments, and by its coarse 

 granules as compared with the much more elegant reniform 

 segments and fine granules of the latter ; neither must the pre- 

 sent plant be confounded with C. hotrytis, which is a very different 

 thins: indeed. But what would seem to set the matter at rest is 

 the very different zygospore of the form now drawn attention to. 

 The present has an orbicular zygospore covered by not very nu- 

 merous, but large and jDellucid hemispherical tubercles, whilst that 

 C. margaritiferum is beset with numerous and elegant forked 

 spines. Nor could it be imagined that the tubercles on the pre- 

 sent zygospore were but rudimentary, and might become event- 

 ually elongated into spines ; for Mr. Archer had now taken this 

 form conjugated at least three times, and from various localities, 



