DESMIDIUM. 253 



The type form of this species has not yet been recorded for 

 this country, and var. cambricum is extremely rare. Both the 

 typical form and the variety seem to be subject to considerable 

 variation in the relative proportions of their cells, and the two 

 examples of var. cambricum figured present a considerable differ- 

 ence of habit ; cf. PL CLXV, figs. 3, 4. The example figured 

 from Loch Fadaghoda (fig. 4) seems to conform more nearly to 

 the typical form in the proportions of its cells, but differs greatly 

 in its chloroplasts. Typical D. coa rotation has only one pyrenoid 

 in the centre of its axile chloroplast. which has about 12 ridges or 

 radiating plates, whilst the specimens of var. c'linbri'-nni from 

 Loch Fadaghoda had a distinctly 1-lobed axile chloroplast, 

 with a pyrenoid in each lobe. It is to be di^iivd that these 

 forms should be examined more thoroughly with regard to the 

 chloroplasts. 



7. Desmidium gracileps (Xordst.) Lagerh. 

 (PI. CLXYI, fig. 5.) 



/// var. f//v/.'//^/x Xordst. in \Viltr. *.V X..r.lst. Al'_r. exsic. 



no. 3>7, 1SSO. 



D. fjnicihji* La^erh. Bidr. Anu-r. I >t.-sm.-fl. 1885, p. 2:28, t. 21. f. :5 : Xnrd-i. 



ML'. X. Zealand, 1888, p. 25; I >e Toni, Syll. Alg. 1889, p. 784; Borg. 



Desm. Brasil. 18! H>. p. 2.'> ; Turn. Alg. E. India. !!>:}, ]. ir.o : \\. & G. 8. 



\\Vst, Al.Lf. C'eyl.ii. l!*n-_>. j,. p.. 4 ; Srott. Fresh- . I'Jankt. 1, 1!03, p. .',.-,2 ; 



Borge, Sao Paulo Sii.-<\\a<--ralL. r . 1918, ]>. 74. 



Cells in front view rotund, about as long as broad, 

 constriction slight, sinus narrow ; semicells shortly 

 pyramidate-truncate, lateral margins biundulate, basal 

 angles acutely rounded, apex truncate ; side view of 

 cell quadrate, rather longer than broad, lateral 

 margins slightly concave. Chloroplasts axile, one in 

 each sernicell, with a central pyrenoid, and 6-8 radiating 

 plates. 



Zygospore subrectangular, provided with a number 

 of short, stout nodules at the two opposite ends only, 

 smooth in the middle part. 



Length 18-24 (JL ; breadth 21-26 ^ ; breadth of 

 isthmus 16-20(jt ; breadth of apex 9-11 [i ; thickness 

 16-18 \L ; length of zygosp. 26-30 ^ ; breadth 22-24 [i ; 

 length of spines about 3-4 k u. ; breadth of spines about 

 2-5 i. 



